With the recent release of MW3, then the chances are, black ops will like all other cods before it, become a distant memory. But zombies as always live on, and the question I ask is what would you like to see in the next zombie game, personally I want a more interactive storyline, a rpg style survival game. Now before you all start complaining this would ruin the experience, I think it would inject a little of that spark zombies needed, for me once we got to the moon I lost the enjoyment of the storyline, the realism of it got me hooked, with Verruckt, Shi No Numa and Der Riese in my opinion being more believable, and if it had been just area 51 then I may have enjoyed it more. Don't get wrong, I enjoyed the Moon, but not as much as Der Riese or Shi No Numa. Also a map without the PaP would be have been a nice twist but anyway Im going to get to my point...
A rpg would allow us to be anywhere on earth, and if its after the 115 missiles left Earth a wasteland then thats even better. Imagine being able to make your own character, and having your own weaponry, obviously ammo would be scarce and you folllow the storyline anyway you liked, helping or hindering richtofen. But imagine the level design, it would be brilliant.
I did enjoy the round aspects of Cod Zombies but it can become too repetitive, the A.I in some cases need to be enhanced to shake things up a little. You can keep most of other aspects of zombies, but one more thing you should at some point be able construct your own weapon (possibly), I on the official board saw some brilliant weapon designs that could be used.
And thats my suggestion, I rambled a bit I admit but its what I think could happen if Treyarch put their minds to it... its their choice though, and I cant gurantee any of you will agree, but its just an idea. Develop, destroy its in your hands now.