Left 4 Dead
Valve's Left 4 Dead is a first person shooter game that offers cooperative elements in both single and multiplayer. You and your team of three buddies end up in a nightmare full of raging zombies - hordes of them. L4D is based on the latest version of Valve's Source Engine which has been used in titles like Counter-Strike: Source and Team Fortress 2 before. There are several incremental improvements in the engine like self shadowing, better fog and lighting effects and post-effect shaders that add to the immersion effect.