I found the Zombies mode in the first Black Ops to be a nice challenge like some kind of neverending bonus round. However, I tended to stay away from it because the skills developed in that game mode didn't lend themselves to the multiplayer objective games that I adored. The zombies in that mode swarm whereas human competitors on Xbox Live tend to cheat and snipe and camp and all that. Learning to deal with one didn't help me with the other.
Now that Call of Duty: Black Ops 2 is confirming Zombies once again with this new trailer, you can put a check in that box and know that BLOPS2 will at least have the same stuff as its predecessor. And I called it back in June: if this Zombies mode doesn't give us zombie Ronald Reagan and/or Qaddafi then this game will be a disappointment after the original Black Ops featured former Secretary of Defense Robert McNamara among others.