My choice for game of the year.
The human vs. infected multiplayer is a blast and very well thought out. The coop works great. Initially when I started playing, I was worried I was going to get bored due to the few maps. Unbelieveably, everytime I play its been a new experience which is probably the most impressive aspect of this game.
Some people think the graphics are dated, (and maybe so) but I think the games looks pretty awesome considering how buttery smooth it plays. I'm playing 2560x1600 8xAA 16xAF with everything on max and it hovers around 80fps most of the time, never dipping below 30 fps with an amd 5600+ windsor, 4g of ram, and 2 260 gtx's in sli so you don't need a big dollar machine to play this game. Exploding zombie heads and blood splattering on the screen will never get old.
The sound is well done and essential to gameplay. You won't do so great playing with sound off...that's for sure.
If there is any complaint I have it's maybe I just want more. More weapons, more maps, and more fun.
This game has my vote for game of the year and it deserves it. It's a very original and well thought out game that makes me glad I'm a PC gamer.