Campaign: Pretty Awesome. I think it's the best campaign out of the series so far. Non-stop action and gameplay.
Zombies: Amazing. Especially if you have all of the available maps. This is my personal favorite feature of the game.
Online Multiplayer: It's got some problems, but nothing I haven't looked past. The maps are pretty cool. Gametypes are more diverse, which increases overall excitement.
If you are used to the ways of Modern Warfare 2, or some other previous game, the online is a new experience. After you unlock a weapon by leveling up, you must also purchase it with in-game money: COD points. New perks, new guns, and new equipment. Pretty cool.
If you're a gamer that likes to shoot things, then you'll enjoy this game a lot.