Single Player story was TERRIBLE. It was like a really bad episode of 24, only you'd be hard pressed to find an episode of 24 as bad as the storyline. Plot was predictable and the whole family loss/drama bs is not something I want in my fps games.
Zombies are terrible compared to how they were in the first BO, zombies break through barriers so fast that repairing them is almost pointless and the overall setup of the maps is just bad.
Multiplayer dosn't seem like a big improvement from MW3. The size of the maps makes it very hard to get much use out of anything other than an smg/shotgun (think mw3 cqb syndrome). I like the original BO and MW2 because the varying maps allowed for frequent use of pretty much every weapon type, whereas now the tight hallways and sharp turns favor the smg and shotgun. Even worse is that in some of my matches, lag compensation was rearing its ugly head.