Oh my god.
I hate shooters. I never play them. But I cannot stop playing Left 4 Dead.
This is probably the best zombie game, best shooter game, I have ever played. Controls are very easy to get used to, and the game never lets the adrenaline stop pumping.
I've grown to shiver whenever I hear pained crying now.
Seriously. Why are you still reading this? If you have a 360 and/or a decent vid card on your PC, go get this game NOW. Download it from Steam, rent it from Gamefly, take a trip down to Walmart, ANYTHING!
The co-op experience is amazing, and the single player mode has the BEST support AI I have ever seen in a game. It is a highly replayable game. No one playthrough is the same. The Director is a sadistic bastard who wants to make your life a living hell. There is no "knowing when something will happen". Shit will hit the fan at any given moment. And heaven help you if a Tank comes and you're in a tiny area, or a Tank comes while there's a Witch in the room.
Also, this game is getting constant 9 and 9.5 scores on websites and magazines. Many people and sites are saying that Resident Evil 4 pales in comparison to this game. It's awesome. Seriously. Go. Get it.