Online Arcade Zombie Fun,
This review is from: Left 4 Dead (Xbox 360) (Video Game)
This game is not perfect, but in terms of sheer fun I struggle to think of a more satisfying effort on 360. If you come looking for Resident Evil, then you will be disappointed. If you come looking for Call of Duty, you will be let down. If you come looking for a truly "Co-Op" game then this is for you. You cannont survive without the other players, you just can't. And the best fun is when you are deciding how to best defend an area from the hoard of zombies you know you are about to attract.
This reminds me of the arcde games of my youth. Fast, fun and not too much exposition. And my girlfriend loves it (and any game that can do that and mean I can play xbox whenever I like with impunity gets my vote).
I would probably steer clear if you don't have Xbox Live though. It's online where this game exists.