Zombies brings the game into complete balance.
Zombies is up to 4 real players V's Ai (something multiplayer misses out on IMO)
The Ai is controlled to get harder and harder (like a traditional game) while challenging the real players to complete tasks at the same time.
From watching the Ghosts reveal I think many elements from Zombie mode has been brought into play like the way you knife people and the revive players in dogtag mode.. It would be a shame to not have any Zombies, maybe they have got a surprise for us zombie fans? I hope so.