Zombies alone is really worth getting it.
The campaign is also very good with the Customization they implemented and the Multiplayer is very good as well.
Zombies blew me away.
I would recommend to just ask for it for christmas?
If you can't do that I would only buy it if you liked MW3 multiplayer and Black ops zombies.
I personally love zombies and am only getting it for that reason alone.
The campaign I heard has alternative endings if thats what you wanted to know.
If you like Cod and Halo you would like BO2. Campaign is very good, they took zombies to the next level, and multiplayer is about the same but the pick ten system makes it better.