Anybody check out the "Undead Nightmare" pack? I think it's pretty good, if not a bit repetitive. Certainly a clever (and funny) departure from the seriousness of the main game, and the online zombie survival mode is fun. There's just not that much variety in the single-player game. Just travel from town to town, cemetery to cemetery, and kill all the zombies.

Still, for 10 bucks, its worth checking out.