I beat a couple campaigns on my friend's PC. It's alright, but my favorite zombie game out now is definitely Killing Floor. It's a simpler premise - you and your squad just have to survive waves of zombies until you all die or you kill the patriarch zombie.
Definitely one of the most brutal games I've ever played, there's a chainsaw and a katana, the music is purely heavy metal, and there's a screen effect to make it look like a grindhouse film. Also a lot of real guns that just feel right - you have to use the iron sights to aim precisely and the recoil is spot-on. I've been using the Mk. 17 a lot since they just added it in the new content patch.
Oh, and Killing Floor is free all this weekend on Steam if you want to try it. My name's Maj. Liability on Steam if you wanna play a game or two.
"Mankind, when left to themselves, are unfit for their own government." - George Washington