"Left 4 Dead is an upcoming multiplayer co-operative survival horror first-person shooter game by Valve Corporation. The game has been built using Valve's Source engine and will be available on Steam and the Xbox 360.

Left 4 Dead pits four human playable or AI controlled survivors of an apocalyptic pandemic against hordes of aggressive "Infected" in a cinematic backdrop in which the players "star" as each character in a fictional movie (eg. No Mercy.) The Survivors' goal is to help each other make it through various scenarios to safety. The Infected are controlled by an AI that dynamically balances difficulty and mood depending on the players' progress and situation. In an alternate game mode, human players can control up to four mutated Boss Infected with special abilities and cooperate to stop the Survivor players.

The expected release date for Left 4 Dead is November 18, 2008 in the United States and November 21, 2008 in Europe to coincide with the tenth anniversary of the release of Half-Life.[5][6] A five minute trailer was released on Halloween.[7] A public demo was released on November 6th for pre-purchasers and will be available for the general public on November 11 for both systems. The demo contains the first one and a half maps of the "No Mercy" campaign and is playable in both single player and multi-player." - Wikipedia