AR: When it comes to realistic POV/FPS games, the Call of Duty franchise is easily one of the most popular across platforms. Good graphics, tight sounds and good battle simulations combine to make it a title worth procuring.
Call of Duty Black Ops Zombies brings the best of the game to Android in all it undead glory.
As far as official canon goes, this is a sequel to Call of Duty: World at War — Zombies (itself a spin-off of a specialized mode in an earlier title). It is set in WWII, and the developer found the one set of antagonists more despicable than Nazis. You guessed right: Nazi Zombies.