Left 4 Dead (L4D) is a new action title from Valve, creators of the Counter-Strike and Half-Life games, and promises to redefine the co-operative genre as those titles did for multiplayer and single player action games.

Set in a modern day survival-horror universe, the co-operative gameplay of L4D casts four "Survivors" in an epic struggle against hordes of swarming zombies and terrifying "Boss Infected" mutants.

Valve’s next generation AI technology, allows for games of 1 to 8 players. Players can play as a Survivor or as one of four types of "Boss Infected," each of whom possess a unique mutant ability such as a 50-foot tongue lasso or a giant belly full of explosive methane gas.

The gameplay takes place across four massive campaigns. The "zombie" population of each mission is choreographed by an "AI Director" that monitors the human players’ actions and creates a unique and dramatic experience for them on the fly.

Set in the immediate aftermath of the highly-anticipated zombie apocalypse, Left 4 Dead features single player, multiplayer and co-operative gameplay modes. Next-generation artificial intelligence tailors the pacing and difficulty ensuring a different experience every time the game is played.

The first L4D DLC - dubbed the L4D Survival Pack -- is due for release this spring and introduces a new multiplayer game mode entitled, Survival, plus two complete campaigns for Versus Mode . A Critic's Choice Edition of the game is also heading to retail stores this spring, and will include access to all the content introduced in the L4D: Survival Pack.

In addition, for PC gamers and aspiring developers, the first Left 4 Dead release for the Source Software Development Kit (Source SDK) will allow the creation of custom Left 4 Dead campaigns that will be discoverable via L4D's matchmaking system. The SDK update is also due for release this spring, and is free of charge to all owners of L4D on the PC.

Xbox Live Title Update:

General

Fixed Survivors being able to climb surfaces marked for versus infected only
Fixed a class of SurvivorBot bugs dealing with rescuing downed players
Players can no longer grab ladders while flying through the air after a Tank punch
Shooting near a car with an alarm that has already fired the alarm will no longer make chirping noises
Fixed mini-gun physics exploit
Fixed propane tanks (and other physics objects) causing players to fall through elevators
Fixed rare achievement bug issues
Fixed several map exploits

Versus Changes
Added HUD elements to show status of other infected players
Fixed instance where a Survivor changing to the infected team would be attacked by infected bots
Normalized special infected melee damage
Fixed exploit where infected players could run away and teleport back to gain health
Players can only change teams once per map
Players can't change teams while other players are still loading
Tank spawns at the same % through the map for both teams in versus mode
Made the Tank and Witch spawn directly on the escape route
Increased chance of getting the Tank or Witch
Fixed team swap issue

Hunter
Easier to pounce a Survivor who is meleeing
Increased Minimum damage a Hunter pounce does

Smoker
Fixed Smoker tongue tolerance
Smoker now has to be killed or the tongue destroyed for the tongue to break
Survivors cannot bash someone off the tongue until the Survivor being pulled is paralyzed or hanging
Tongue attacks that fail to paralyze or hang a Survivor will use the shorter ability delay timer
Fixed cases where the ability timer was not using the correct time
Fixed case where you could point at a Survivor but not register a tongue hit
Fixed Smoker tongue not targeting and landing properly through PZ ghosts
Smoker tongue does damage every second while dragging paralyzed Survivors

Tank
Bashable objects now appear with a red glow
Tanks hitting a car with an alarm disables the alarm permanently
Tank frustration timer is only reset by hitting Survivors with rocks or fists
Reduced autoshotgun damage against Tanks

Witch
Witch spawns at the same % through the map for both teams
Avoids spawning within a certain % of the tank
Fixed an exploit where the Witch could be woken up and tricked into attacking Survivors

System Requirements:

• OS: Windows Vista, XP or 2000
• CPU: 3.0 GHz P4, Dual Core 2.0 or AMD64X2 (or higher)
• RAM: 1 GB for XP / 2GB for Vista
• Disc drive: DVD-ROM Drive
• Hard drive: At least 7.5 GB of free space
• Video: Direct X 9 compatible video card (Video card must be 256 MB or more and should be a DirectX 9-compatible with support for pixel shader 2.0)
• Sound: Direct X9.0c compatible sound card

Left 4 Dead is currently available on PC and Xbox 360.