Released: 2008
Developer/Publisher: Valve for EA/Valve
Platform(s): 360, PC

The only way to survive the zombie apocalypse in this disturbing cooperative FPS is to kill in concert with three other survivors (and not accidentally buck them down). There's no "i" in team, but there are two in "eaten alive by zombies." And three in "fucking sick shit!"

Artificial intelligence detects how easily you're advancing and will adjust the number and type of zombies attacking you to keep things interesting.