Turtle Rock Studios, the same people behind Counter Strike: Condition Zero have announced a new multiplayer co-operative (oh yes!) survival horror game called Left 4 Dead. The game will utilize Valve’s Source engine and will primarily revolve around four people as they strive to survive a zombie outbreak (hence the name).
Designed for co-op play, the four players must work together to finish each stage of the game, lending each other artillery support, sharing ammo and rescuing each other when zombies are on top of them. In addition to the standard four players as humans, another four players can be amongst the masses of assaulting zombies, seeking to take down the other players. Zombie players might even find themselves become one of the four mutant "boss" zombies, who have unique powers that can be used to devastate, injure, tie up, mark and track, confuse, or even humiliate the gun-toting human survivors.
Although no concrete release date’s out till now, expect the game sometime this year.

