"The zombie apocalypse. Be honest: You've thought about it. When most humans have been turned into shambling, flesh-hungry monsters, how will you fare? Whether you fancy yourself an intrepid survivor or an infected savage, Left 4 Dead is the game for you. Battling your way through the grim, desolate world is always tense and challenging, thanks to the unpredictable, relentless enemies. It's equally thrilling to play as one of the zombies (aka the infected), coordinating deadly ambushes as you try to kill the survivors. Nevertheless, Left 4 Dead's well-crafted gameplay simply must be experienced in multiplayer. Human teammates (or enemies) make each play-through dynamic, mitigating the game's two hang-ups: limited map selection and uninspired friendly AI. Despite these hitches, Left 4 Dead is a remarkably fun, excitingly tense game that will make you want to revisit the apocalypse again and again. "
I have seen the demo. My brother and his friends were playing it and let me tell you that the zombies are fast not your typical slow ones. This game has a "28 Days Later" feel to it and it scared the crap out of me. The Intro to the game is here( warning foul language and blood): http://www.youtube.com/watch?v=Nbzyt79iSR0