Left 4 Dead

Left 4 Dead is a cooperative first-person shooter video game. It was developed by Turtle Rock Studios, which was purchased by Valve Corporation during development. The game uses Valve's proprietary Source engine, and is available for Microsoft Windows, Xbox 360 and Mac OS X. Development on the game was completed on November 13, 2008, and two versions were released digitally: A downloadable digital version, released on November 17, 2008, and a digital retail disc version, with a release date determined by region. The digital retail disc version was released in North America and Australia on November 18, 2008; and in Europe and Japan on November 21, 2008.

Set during the aftermath of an apocalyptic pandemic, the game pits its four protagonists—dubbed the "Survivors"—against hordes of the infected. There are four game modes: a single-player mode in which allied characters are controlled by AI; a four-player, co-op campaign mode; an eight-player online versus mode; and a four-player survival mode. In all modes, an artificial intelligence (AI), dubbed the "Director", controls level pacing and item placements, in an attempt to create a dynamic experience and increase replay value.

Left 4 Dead was well received by the industry media upon its release, with praise given for its replay value, focus on cooperative play, and movie-like experience. Several criticisms were aimed at limited level selection and the lack of a narrative. The game has won several publication awards, as well as distinctions from the Academy of Interactive Arts & Sciences and British Academy of Film and Television Arts. As was done with Team Fortress 2, Valve supplemented the game with free downloadable content. The first, called the "Survival Pack", was released on April 21, 2009. The second piece of DLC was charged for on Xbox Live and came in the form of a new Campaign entitled "Crash Course," released for both the PC and Xbox 360 on September 29, 2009.

Plot
Pennsylvania suffers an outbreak of "Green Flu"; a highly contagious virus causing extreme aggression, mutation to the body cells, and loss of higher brain functions. Two weeks after the infection four immune survivors— Bill, a Vietnam veteran; Zoey, a college student; Louis, an IT analyst, and Francis, an outlaw biker— make their way through the city of Fairfield, only to discover that the virus is creating more dangerous mutations. After narrowly avoiding these new infected, along with hordes of others, the survivors are alerted to the presence of an evacuation point at the nearby Mercy Hospital roof by a passing helicopter. Fighting their way through the city's streets, subway and sewers, they are rescued from the hospital's roof by the pilot, only to discover he is infected.

With Zoey forced to kill the pilot, the helicopter crash lands in an industrial district outside the city. Finding an armored delivery truck, the group uses it to make their way to the town of Riverside. However, they find the road blocked, and travel the rest of the way on foot. After an encounter with an infected lunatic in the local church, they discover that the town is overrun, and decide to head to a nearby boathouse for rescue. Contacting a small fishing vessel, they manage to reach the city of Newburg on the other side of the river, only to find much of it in flames. Seeking cover in a large greenhouse, their rest is interrupted when a military C-130 Hercules passes overhead, leading the survivors to travel through the city's business district towards Metro International Airport. Upon arrival, the group see that in an attempt to contain the infection, the military had bombed the airport while infected pilots crash planes in an attempt to land; the runway however is largely intact, allowing the survivors to fuel up and escape in a waiting C-130.

Despite this apparent rescue, it crashes as well, and the survivors once again find themselves alone on the outskirts of Allegheny National Forest. Following a series of train tracks through the area, the group find themselves at a functioning, but abandoned, military outpost. After answering a radio transmission, the survivors make their final stand against hordes of infected, before a military APC arrives to transport them to Northeast Safe Zone Echo, supposedly the only uninfected area yet to be overrun. Instead, they are kept at a military installation and informed that even though they are immune, they still carry the virus. They are temporarily held by the military before the base is overrun with infected. The four escape via train and travel south at Bill's insistence; Bill believes that they can find long-term safety from the infected on the islands of the Florida Keys.

At the portside town of Rayford, they find a boat but must raise an old rusty bridge powered by an aging generator to get the boat into open waters, assured that the machinery noise will alert a large horde. When Louis is injured and unable to move quickly, Bill sacrifices himself against the horde to make sure the generator keeps running and allowing the three to stay clear of the horde. After waiting for the horde to disperse, the three remaining survivors are taking time to mourn Bill's death when they encounter the four survivors from Left 4 Dead 2, who need to cross the bridge to continue to the west. Zoey, Louis, and Francis help the four to get across and fend off another horde as they lower the bridge, and then set sail for the Keys.

Gameplay
Left 4 Dead is a first-person shooter. In campaign mode, the player takes control of one of the survivors; if four human players are not available, then the remaining survivors are AI-controlled bots. They play through the levels fighting off the infected—living humans who have been infected with a rabies-like virus that causes psychosis The survivors are carriers of the disease, so they do not show signs of any symptoms.

The game is focused on cooperation and team play and thus eschews some "realism" conventions usual in most FPS games of the wider genre; colored outlines of teammates are visible through walls to help players stick together and coordinate their movement. If a survivor falls off a ledge, then they may automatically hang onto it and can only be helped up by another survivor. If a survivor's health is depleted, then they become incapacitated and can only be revived by another survivor, at which point they continue playing with a low amount of health that decreases over time. If a survivor has been incapacitated and revived twice without tending to their wounds, then they will experience distorted black-and-white vision, and the next incapacitation will kill the character. If a survivor takes enough damage while incapacitated, or is not eventually helped up by teammates, then the incapacitated character will die. During "Campaign" mode, if a survivor is killed, then they will respawn in a closet or other enclosed space after a period of time (except during key points in the scenario), but must be freed by another survivor to rejoin the team. Otherwise, the player must wait until the next level. However, if all human player survivors are killed or incapacitated, players will have to restart from the last checkpoint. Survivors can share first-aid kits and pain pills and help each other heal. Left 4 Dead has friendly fire (which causes no damage on the easy difficulty mode), increasing the need for caution around other survivors.

The survivors communicate by voice commands that are accessed by quick menus, and some may sound off automatically when performing actions such as reloading or spotting infected. Over 1,000 unique lines have been recorded for each survivor. Additional communication of player actions is conveyed through character lights. Also, weapon-mounted flashlights and muzzle flashes help the players in determining whether their companions are shooting, performing melee attacks, reloading or moving. Due to control issues and the likelihood of players using a headset, the Xbox 360 version of Left 4 Dead omits the quick phrases feature.

The game is experienced through five campaigns that take place in various urban and rural locales. Multiple visual in-game hints—including license plates, park signs, markings on airport equipment, and lines of dialogue spoken by the survivors—suggest that these locations are in Pennsylvania, and similarly a memorial wall giving names of those who have died in the infection (actually names of the game's development team) along with their dates of birth and death suggests that the game takes place in October 2009. Each campaign is divided into five chapters (except Crash Course, which has two chapters) marked by safe rooms, which are checkpoints where players can heal, re-arm and revive characters who were killed. Specifically, the four campaigns are: "No Mercy", an urban setting culminating in a hospital skyscraper; "Death Toll", a small-town and countryside setting; "Dead Air", an airport setting; and "Blood Harvest", a woodland and farm setting. A two-level campaign, "Crash Course", was released on September 29, and is set in the outskirts of a small industrial town. The levels have distinct beginnings and ends, but there are a number of alternate routes to follow with more supplies, helping to create a sense of non-linearity. In the final chapter of each campaign, the players must defend a position from an onslaught of infected until rescue arrives. Each campaign typically lasts between 20 and 75 minutes depending on the difficulty level. Both platform versions of the game utilize an achievement system.

Survivor Characters
There are four playable human characters in the game: Francis, a stereotypical biker (voiced by Vince Valenzuela); Bill, a Vietnam Veteran (voiced by Jim French); Zoey, a university student (voiced by Jen Taylor); and Louis, a district Account Manager (voiced by Earl Alexander). Louis' profession is now listed as a Junior Systems Analyst in the IT department for Franklin Brothers in Philadelphia, keeping in line with the comic released for "The Sacrifice" DLC. Early plans were for players to be randomly assigned to characters but in the final release, players can choose any character—provided that the character has not already been selected—or be randomly assigned an unselected character. Aside from appearances, all of the characters have identical abilities in-game.

Weapons
Survivors are armed with various firearms. Each player starts the game with a semiautomatic pistol. It may be reloaded an unlimited number of times and is the only weapon that the survivor can use when they are incapacitated. When a second pistol is found, the player can dual wield them, also with unlimited ammo. At the beginning of each campaign, the player can choose between a submachine gun and a pump-action shotgun. As the survivors progress through a campaign, more powerful weapons can be found: the fully automatic assault rifle (an upgrade to the submachine gun), a semi-automatic shotgun (an upgrade to the pump-action shotgun), and a scoped hunting rifle. A flashlight that can be toggled on and off is mounted on each firearm, with the exception of additional pistols. In addition to firearms, a player can also carry three other items in their inventory: improvised grenades (either a Molotov cocktail or a pipe bomb modified with an attached smoke alarm designed to attract the infected to it before it explodes); a first aid kit, which can be used to heal any survivor and pain pills, which provide temporary health that depletes gradually and quicker with damage from infected, and can be handed to teammates for later use. Regardless of what weapon or item a player is using, a melee attack can be used to shove away any infected within reach. Also available are environmental weapons, such as gas cans, propane cylinders, and oxygen tanks, all of which explode when shot. These environmental weapons can be picked up, moved, and used as a melee weapon by the survivors, but while carrying an object they cannot use their weapons or health items. Strategically placed minigun turrets are also encountered at various locations throughout the different maps.

Infected Characters
The infected (voiced by experimental musician Mike Patton and voice actor Fred Tatasciore) are the survivors' foes in Left 4 Dead, and they appear to be partly inspired by the infected from several modern films, including Dawn of the Dead, 28 Days Later, or Quarantine. An important distinction from the former is that while the infected do resemble traditional undead zombies, they are, as cited in the game's manual, living humans infected with a rabies-like pathogen, very much like the infected in the later two films. While they are never seen eating human flesh or brains, multiple 'survivors' who have been killed by the infected appear throughout the game, and appear to have been partially eaten. In The Sacrifice comic, Zoey's mother is bitten in the face. She then begins to attack the rest of her family. One such victim can be heard saying "I can't believe he bit me!" before being encountered later on, fully infected. In an interview with 1Up.com, Mike Booth commented on the concept of using a pathogen as an inspiration for the setting: The common infected encountered during the game are fast and agile, weak individually, but may be overwhelming in numbers. They display a special attraction to high-pitched alarm-type sounds, such as the beeping device attached to pipe bombs and car alarms. Common infected will often chase down the source of these noises while ignoring lower-pitched, but much louder sounds such as gunfire. They occasionally attack in masses referred to in-game as a "horde".

In addition to the common infected, there are five "special" or "boss" infected whose mutations grant them special attacks that make them far more dangerous. Each of the special infected, as well as approaching hordes, have a distinctive sound or a timely musical cue, making their presence easily recognizable by players. There are five special infected in Left 4 Dead. In versus mode, four additional players can take control of the special infected—apart from the witch, who remains computer-controlled. Each infected player is randomly assigned a class of special infected when they enter a spawn mode. While in spawn mode, the infected can quickly roam around the map in search of an appropriate place in which to spawn. This location must be sufficiently distant from any survivor, out of the line of sight of any survivor, and outside restricted areas such as safe rooms. Upon death, the infected player must wait up to 10–25 seconds before re-entering spawn mode, depending on how many players are on the infected team. When a tank is spawned in the game, infected players receive a message indicating which player will control it. The human-controlled infected can see their teammates' outlines through walls similar to the survivors, but can also see each survivor's outline, which is colored according to the survivor's health and fades out if the survivor refrains from attacking, running and vocalizing. Vertical pathways exclusive to the infected, such as pipes and vines, are marked with animated symbols for the infected players. These can be climbed and used for ambushes.
 * The Boomer is a bloated infected that can spit vision-impairing bile on the Survivors, attracting hordes of infected, and explodes on death, spewing more bile in the immediate area. They emit burping and vomiting like sounds when close by. A 5-note double bass cue plays to warn of the Boomer.
 * The Hunter is an agile foe that can jump and pounce on a survivor, and then tear at his victim until he is knocked off, kills his prey or is killed. A hunter emits animal like screeches or light roars when close by, and a snarling growl can be heard when in close proximity. The Hunter is signaled by a startling high pitched piano cue.
 * The Smoker is a boil-covered creature with a long tongue that it uses to ensnare and drag a survivor back to himself. It may then either attack the survivor directly, allow the horde to attack him, or leave the survivor suspended over a cliff or roof-edge. The Smoker only releases its victim if a teammate shoves the ensnared survivor, if the tongue is shot, the survivor is killed, or upon the Smoker's death, which results in an explosion that leaves a vision-obscuring cloud. Smokers have raspy voices and frequently wheeze and cough, presuming that they may have been an avid smoker before becoming an Infected. A 2-note low piano cue signals the Smoker.
 * The Tank is a gigantic muscular infected that has the ability to swipe at survivors, knocking them off their feet and incapacitating them; it can also knock cars and other debris into the survivors. The Tank is the most durable of all the special infected, and requires the full support of all of the survivors in order to be killed. The Tank is accompanied by a booming orchestral score to signal his appearance.
 * The Witch is a female infected with long claws that stays crying in one spot. Survivors can often avoid the Witch but if they disturb her with light, loud noises or gunfire, she will become aggressive and charge at the one who "startled" her. Along with crying, an eerie choir tune plays when she is near. The Witch has the strongest attack of the infected in the game; able to kill a survivor outright with one blow on the hardest difficulty. As such she is never playable by human players in Versus mode.

Another special character, the "Screamer" was an infected tied to a straight jacket and heard by its maniacal cackling. He would not attack, but would run away if spotted and when he found a safe hiding place, he would emit a scream that would attract a horde of zombies to attack the survivors. The directors soon found him to be stressful, especially if he was in a crowd, so they removed him from the game. His horde-attracting power later turned into the Boomer's vomit attack, which they found to be fitting due to the Boomer's obese image.

AI Director
The artificial intelligence of Left 4 Dead features a dynamic system for game dramatics, pacing and difficulty called the "Director". Instead of fixed spawn points for enemies, the Director places enemies and items in varying positions and quantities based upon each player's current situation, status, skill and location, creating a new experience for each playthrough. The Director also creates mood and tension with emotional cues, such as visual effects, dynamic music, and character communication.

Valve has termed this dynamic set-up "procedural narrative". In addition to the AI Director, there is a second Director that controls music. It was created as a way to keep the music interesting throughout the game. The music Director monitors what a player has experienced to create an appropriate mix. The process is client-side and done by a multi-track system. Each player hears their own mix, which is being generated as they play through the game, and dead players watching a teammate hear their teammates' mix.

Game Modes
Left 4 Dead contains four game modes: campaign, versus, survival, and single-player. The cooperative campaign consists of up to four human-controlled survivors who attempt to make their way between safe rooms and eventually to rescue. In this mode, the special infected are controlled by the AI. In a versus campaign, each team of one to four players plays each chapter of the campaign as both survivor and infected, swapping sides once per chapter. Unlike campaign mode, dead survivors do not respawn. If at least one player-controlled survivor finishes the level, the survivor team earns 100 points as well as bonus points based on their health and the health items in their inventory. These points are then multiplied by the chapter's difficulty level, and the number of survivors who finished. If all player-controlled survivors are killed, the survivor team only earns points according to their average progress through the chapter and the difficulty multiplier. Survival mode consists of a timed challenge where players try to survive as long as possible against a never-ending flood of the infected, added in April 2009 in the Survival Pack downloadable content. Single-player mode is similar to campaign mode, but played offline with three AI-controlled bots as the other survivors. On Xbox 360, other players can join in on the same console to turn single player into an offline co-op game. The game can also be played through a system link, or local area network. Players have also discovered a way to do splitscreen co-op play with the PC version.

Production
Development on Left 4 Dead started in mid-2005. Turtle Rock Studios aimed to create a horror film-inspired game that merges single player games' character-driven narrative structure with multiplayer games' social interaction and high replayability. The game was first revealed in the Christmas 2006 publication of PC Gamer UK with a six-page article describing a playthrough at Turtle Rock Studios headquarters. A teaser was released with The Orange Box. The game was first playable at the Showdown 2007 LAN in San Jose and at QuakeCon 2007. Turtle Rock Studios announced Left 4 Dead on November 20, 2006, and was acquired by Valve Corporation on January 10, 2008, because of the game and long-standing relationship between the companies. The game opened up to pre-purchasing on Valve's Steam system on October 15, 2008.

To give Left 4 Dead significant exposure, Valve financed a $10-million marketing campaign for the game in the United States and Europe, with advertisements appearing on television, print, websites and outdoor placements in many cities. Valve also hosted photo contests called, "Dude, where's my thumb?" offering copies of Left 4 Dead to people who submitted the best picture involving zombies or the outdoor advertising.

Development
Left 4 Dead uses the 2008 version of Valve's Source engine, with improvements such as multi-core processor support and physics-based animation to more realistically portray hair and clothing, and to improve physics interaction with enemies when shot or shoved in different body parts. Animation was also improved to allow characters to lean realistically when moving in curved paths. Rendering and artificial intelligence were scaled up to allow for a greater number of enemies who can navigate the world in better ways, such as climbing, jumping, or breaking obstacles.  Lighting was enhanced with new self-shadowing normal mapping and advanced shadow rendering that is important to convey information about the environment and player actions.  Wet surfaces and fog are used to create mood.  Many kinds of post processing cinematic visual effects inspired by horror movies have been added to the game. There is dynamic color correction that accentuates details based on importance, contrast and sharpening to focus attention on critical areas, film grain to expose details or imply details in dark areas and vignetting to evoke tension and a horror-film look.

Left 4 Dead underwent many phases of development; influenced by playtesting, Turtle Rock Studios removed many of the features that were originally in the game. In the initial phases, there was another special infected, called the "screamer", which had no attacks but upon spotting a survivor would run to a safe place and then emit a loud scream that attracted a horde of infected. This infected class was removed, but its ability to attract the horde was incorporated into the boomer's vomit. A persistent merit/demerit system was envisioned to provide positive feedback for good behavior, such as aiding a fallen teammate; and negative feedback for poor behavior, such as shooting a teammate. This would provide a score to rank a player's effectiveness as a teammate, but this system was removed late in the development of the game in favor of immediate, non-persistent feedback displayed in-game. Another significant element removed was a long introduction between campaigns; because the game is designed for replayability, it was difficult to hold the player's attention for repeated viewings of cut scenes, so they were dropped in favor of a sparse narrative. Also, the game started out with one big city design with many routes for the survivors, but playtesters were confused when they began to play, and later they always chose the same route; ultimately Turtle Rock Studios cut the city maps into the first "No Mercy" and "Dead Air" campaigns.<sup class="reference" id="cite_ref-48">

Certain Affinity assisted Turtle Rock Studios with the Xbox 360 version of the game.<sup class="reference" id="cite_ref-49"> The Xbox 360 version of Left 4 Dead has the same game modes as the PC version but has additional features such as support for Split screen, allowing for two players to play offline and online from the same console,<sup class="reference" id="cite_ref-1up_20080828_50-0"> and System Link play.<sup class="reference" id="cite_ref-51"> Split-screen mode can also be achieved on the PC version, but it requires console commands and may require the modification of controller configuration files; and it is not officially supported.<sup class="reference" id="cite_ref-52"> Both versions of the game have a new matchmaking system to simplify the process of finding other players.<sup class="reference" id="cite_ref-making_of_e3_video_9-5"> <sup class="reference" id="cite_ref-53"> This new server management system was met with a negative reaction from PC server operators, who, with this system, had very little control over their servers. This led to Valve releasing a series of patches that allowed server operators to remove their server from the matchmaking "pool" of servers or make private servers.<sup class="reference" id="cite_ref-54"> Valve runs dedicated servers for both versions of the game.

Promotion
To promote the game and provide basic training to players before starting the game, Valve chose to develop a pre-rendered intro movie. This movie was released on Halloween<sup class="reference" id="cite_ref-56"> and shows events prior to the beginning of the "No Mercy" campaign.<sup class="reference" id="cite_ref-intromovieblog_57-0"> Valve chose an intro movie over in-game training mechanics because they wanted the players to be immediately dropped into a zombie apocalypse. Valve later detailed in their official Left 4 Dead blog how they designed the movie, from an intentionally very basic animation in the beginning of July 2008 to the final result for the launch of the game.<sup class="reference" id="cite_ref-intromovieblog_57-1">

Early access to the Left 4 Dead demo for people who pre-ordered the game began on November 6, 2008, for both Windows and Xbox 360. It gave users access to both online and single-player play in two "scenes" in one "movie" within the game. This promotion was being offered in addition to the ten percent savings for those who pre-order and applies to all Steam Windows pre-orders and all Windows and Xbox 360 pre-orders from GameStop and EB Games in North America.<sup class="reference" id="cite_ref-58"> On November 11, the Left 4 Dead demo was made available to all Windows and Xbox 360 gamers worldwide.<sup class="reference" id="cite_ref-59"> The Left 4 Dead demo was removed from the Xbox 360 Marketplace and Valve's own Steam after the game's release on November 18, 2008, however it is still available for those that played it.

The demo had many server problems when it launched, primarily Valve's strategy for server management which made it impossible to set up a dedicated private server with administrator controls.<sup class="reference" id="cite_ref-ars_technica_demo_review_60-0"> However, a stream of patches led to the availability of a server browser and basic private server functionality as well as Valve's acknowledgment of player concerns.<sup class="reference" id="cite_ref-ars_technica_demo_review_60-1"> It appears that a patch released just before the game itself has resolved many of the connection issues that demo players were having.<sup class="reference" id="cite_ref-Left_4_Dead_server_update_61-0">

On May 1, 2009, the game was released freely via Steam as a one-day trial called "Freaky Free Friday". The trial was then extended to end on Saturday.<sup class="reference" id="cite_ref-62">

On October 5, 2010, the price of the game via Steam was dropped to $6.80 USD, or a "4-pack" for $20.40, as a promotion coinciding with the release of "The Sacrifice" DLC.

Release
Left 4 Dead went gold on November 13, 2008, and was released on November 18, 2008, in North America; and on November 21, 2008, in Europe to coincide with the tenth anniversary of the release of Half-Life.<sup class="reference" id="cite_ref-steam_64-0"> <sup class="reference" id="cite_ref-65">

Valve released a server patch in December 2008 to stop players on Xbox Live from using PC-style cheats.<sup class="reference" id="cite_ref-66"> A spokesman from Valve said, "The fix is designed to halt the cheating behavior on the dedicated servers, which accounts for the majority of the co-op and versus modes of play."

After Release
Valve intends to support the PC version of the game through free content updates and the Xbox 360 version with DLC.<sup class="reference" id="cite_ref-Left_4_Dead_DLC_68-0"> On a podcast by Kotaku, writer Chet Faliszek divulged that an announcement regarding DLC for the PC and Xbox 360 would be released "very soon", and that the announcement was delayed by the holiday season. On February 5, 2009, Valve released details about the upcoming downloadable content pack. The two full campaigns of "Death Toll" and "Dead Air" for versus mode—which were previously unavailable—are included, as well as the survival game mode, where the survivors try to survive endless waves of the infected for as long as possible. On February 11, 2009, Valve announced that the downloadable content for the game would be free for both the Xbox 360 and PC;<sup class="reference" id="cite_ref-69"> and on April 21, it was released.<sup class="reference" id="cite_ref-70"> Survival mode shipped with 16 maps, 15 of them being modified portions of existing maps and one being a new lighthouse-themed level titled "The Last Stand".<sup class="reference" id="cite_ref-IGN_L4D_DLC1_32-1"> A Game Of the Year Edition of Left 4 Dead was released on the PC and Xbox 360 on May 12, 2009, with updates and new content included on the disc.<sup class="reference" id="cite_ref-objects1_71-0">

On May 15, 2009, an open beta test for the Source Development Kit updated to support Left 4 Dead was started under the name of the "Left 4 Dead Authoring tools". This included a new set of plugins that allowed for users to import data from SketchUp, a free 3D modeling program, directly into the Hammer level editor for use in maps.<sup class="reference" id="cite_ref-SDK_Beta_72-0"> The beta was concluded on June 25, 2009, with the full release of the Left 4 Dead authoring tools and corresponding server and matchmaking update to support custom maps. The update included a command line tool for packaging custom Left 4 Dead campaigns to ease distribution.<sup class="reference" id="cite_ref-73">

A sequel, Left 4 Dead 2, was announced at the 2009 E3 conference and was released November 17, 2009.<sup class="reference" id="cite_ref-74"> Addressing concerns voiced by fans, Gabe Newell responded to an email from Kotaku explaining that despite the upcoming sequel, Left 4 Dead would continue to be supported and more content is planned in the coming months.<sup class="reference" id="cite_ref-75">

On August 4, 2009, Valve announced the second DLC pack. It contains a new campaign called Crash Course, set shortly after the events of the No Mercy campaign, where the Survivors try to get to a Truck Depot after the helicopter they were in crashed. It is available for co-op, versus and survival modes, with various tweaks to game mechanics, and containing new locations and character dialog.<sup class="reference" id="cite_ref-76"> The DLC was announced to be released on September 29, 2009,<sup class="reference" id="cite_ref-79"> on which date it was released for free for PC, but was accidentally released on Xbox Live for 800 Microsoft Points instead of the previously announced price of 560 Microsoft Points. The price was amended soon after, and all players who bought the DLC for 800 points were refunded 240 points.<sup class="reference" id="cite_ref-80">

On November 9, 2009, a matchmaking update to allow for matchmaking between teams of four players in versus mode was released.<sup class="reference" id="cite_ref-81"> <sup class="reference" id="cite_ref-82">

An add-on campaign for Left 4 Dead 2, "The Passing", featured the Left 4 Dead survivors meeting the new cast as part of a full campaign. The Left 4 Dead 2 content was set for release in March 2010, however it was delayed until April 22, 2010. To connect the events in "The Passing" to that in Left 4 Dead, Valve released another add-on in October 2010 for both Left 4 Dead and its sequel, entitled "The Sacrifice"; the events of the add-on take place before "The Passing" and tells how the Left 4 Dead survivors come to encounter the group from Left 4 Dead 2, and how one sacrificed themselves for the safety of the others.<sup class="reference" id="cite_ref-l4d2_sacrifice_83-0"> <sup class="reference" id="cite_ref-gttv_passing_85-0">

Valve announced a 190 page digital comic that has been revealed in four parts in the weeks leading up to the release of The Sacrifice.<sup class="reference" id="cite_ref-86"> Part one was released on September 14, 2010,<sup class="reference" id="cite_ref-87"> with a new part scheduled for release each week until The Sacrifice's October 5 release.<sup class="reference" id="cite_ref-88"> The comic is illustrated by Mike Oeming, the artist behind the Powers comic series,<sup class="reference" id="cite_ref-89"> and tells the stories of the original four survivors, as well as the events leading up to the infection. The comic begins with Bill, having just sacrificed himself to save the others, taking on three tanks while severely wounded. It then cuts to the finale of Blood Harvest, which is revealed to be one week earlier. In The Sacrifice DLC, any player, whether playing as Bill or not, can choose to sacrifice themselves to allow the other survivors to complete the campaign.

In March 2010, Valve announced that it would be bringing the Steam content platform to Mac OS X computers; along with it, they will be providing native versions of existing Valve games including Left 4 Dead and its sequel. The game was released for Mac OS X on October 27, 2010<sup class="reference" id="cite_ref-90"> Left 4 Dead support cross-platform play, allowing Mac players to play alongside PC players on the same servers, and is also part of the "Steam Play" cross-compatible and Steam Cloud titles, allowing a player that has purchased the game on one platform to download and play it on the other platform for free.<sup class="reference" id="cite_ref-91">

Critical Reception
Left 4 Dead received mostly positive reviews from critics. On GameRankings, the game received aggregated scores of 89.24% and 89.19%, on Xbox 360<sup class="reference" id="cite_ref-GRX360_92-1"> and PC<sup class="reference" id="cite_ref-GRPC_93-1"> respectively, and a score of 89 out of 100 for both Xbox 360<sup class="reference" id="cite_ref-MCX360_94-1"> and PC<sup class="reference" id="cite_ref-MCPC_95-1">, on Metacritic. IGN stated, "It's almost pitch perfect in how it captures the tension and the action of a Hollywood zombie movie", and went on to describe it as, "quite possibly the perfect co-op shooter."<sup class="reference" id="cite_ref-L4Dreview-IGN_100-1"> Giant Bomb commented that the Source engine was beginning to show its age, but praised the game's use of lighting and filmic effects that gives the game world, "a desolate, washed-out feeling", as well as the realistic and emotive faces and the engrossing art direction.<sup class="reference" id="cite_ref-L4Dreview-Giant_Bomb_105-1"> Eurogamer concluded that Left 4 Dead "is another deeply professional, personality-filled and progressive take on the shooter from Valve."<sup class="reference" id="cite_ref-L4Dreview-Eurogamer_97-1"> Both IGN and GameSpot praised the game's replayability, but Gamespot criticized the "limited map selection" that could "sometimes feel a bit repetitious".<sup class="reference" id="cite_ref-L4Dreview-Gamespot_30-2"> <sup class="reference" id="cite_ref-L4Dreview-IGN_100-2"> GameSpy noted the lack of an overall narrative between the campaigns was disappointing.<sup class="reference" id="cite_ref-L4Dreview360-Gamespy_99-1"> However, some reviewers praised its faithfulness to the zombie film genre,<sup class="reference" id="cite_ref-106"> including the "deliberately ambiguous" back-story,<sup class="reference" id="cite_ref-109"> and the amount of characterization and emotion brought by each of the four survivors.<sup class="reference" id="cite_ref-110"> TeamXbox commented that clipping issues hurt the otherwise "incredibly good" visual experience.<sup class="reference" id="cite_ref-L4Dreview360-Teamxbox_103-1"> Hideo Kojima, creator of the Metal Gear series declared in an interview to 1UP.com that he was "addicted to the game", which was, in his view, one of the "core titles made with movie-industry people that explore the depths of hi-def".

Sales
On October 28, 2008, Valve reported that preorders for Left 4 Dead had beaten those of The Orange Box by 95 percent after the Steam pre-order was launched.<sup class="reference" id="cite_ref-112"> On November 21, 2008, the day of the game's release in Europe, Valve issued a press release stating that Left 4 Dead had exceeded the pre-order numbers of The Orange Box by over 160 percent.<sup class="reference" id="cite_ref-113"> The Xbox 360 version of Left 4 Dead was the seventh best-selling game of December 2008 in the United States, selling in excess of 629,000 copies.<sup class="reference" id="cite_ref-gamedaily_114-0"> On February 3, Electronic Arts revealed that Left 4 Dead had sold 1.8 million copies, excluding Steam and worldwide sales figures.<sup class="reference" id="cite_ref-115"> On March 26, Mike Booth revealed that the game had exceeded 2.5 million sales at retail during a presentation at the Game Developers Conference 2009.<sup class="reference" id="cite_ref-116"> On September 24, 2009, Valve announced that almost 3 million copies of the game had been sold.<sup class="reference" id="cite_ref-117"> On May 10 2011, Doug Lombardi mentioned that the game and its sequel have each sold 3 million copies on the Xbox 360.<sup class="reference" id="cite_ref-118"> On August 11 2011, in a phone interview with Giant Bomb, Chet Faliszek said that the series has sold over 11 million units in total.

Awards
Left 4 Dead received recognition as one of the best multiplayer and PC games of 2008 from various organizations and gaming publications. The game was named the Best Multiplayer Game of 2008 by IGN,<sup class="reference" id="cite_ref-120"> GameSpy,<sup class="reference" id="cite_ref-122"> Spike TV,<sup class="reference" id="cite_ref-123"> NoFrag<sup class="reference" id="cite_ref-124"> and BAFTA;<sup class="reference" id="cite_ref-125"> and as the Computer Game of the Year by the Academy of Interactive Arts & Sciences (AIAS),<sup class="reference" id="cite_ref-126"> Spike TV, and Bit-tech.<sup class="reference" id="cite_ref-127"> Other awards include Outstanding Achievement in Online Gameplay from the AIAS, Best Use of Sound for the PC<sup class="reference" id="cite_ref-128"> and Best Shooting<sup class="reference" id="cite_ref-129"> game overall from IGN, Father of All FPS from Nofrag, and the best Cooperative Multiplayer<sup class="reference" id="cite_ref-130"> and Shooter<sup class="reference" id="cite_ref-131"> of 2008 from GameSpot who also nominated it for Game of the Year.

Links

 * "Left 4 Dead Review". IGN.
 * "Left 4 Dead Review". GameSpy.
 * "Left 4 Dead". Official Xbox Magazine.
 * "Left 4 Dead Review (Xbox 360)". TeamXbox.
 * "Left 4 Dead Review". Game Informer.
 * "Left 4 Dead Review". Giant Bomb.
 * "Left 4 Dead Sells 1.8 Million at Retail". Shacknews.
 * Left 4 Dead official website
 * Left 4 Dead on Steam
 * Left 4 Dead Wiki