You couldn't milk a cash cow better then this series has been.
The progressiveness of the multiplayer experience is really gone, its shrunk to a run and gun madness fest worse then ever noted in any of the prequels before. It's no wonder Call of Duty 4: Modern Warfare has the biggest following of any of the titles to date. The cash cow although beginning to show signs of shrinking is still being milked for every penny's worth. Black Ops II couldn't be a bigger disappointment (Actually It could be). You cannot host your own servers but instead follow disastrously in the footsteps of Modern Warfare 2 with Peer to peer connections an unsteady mess of bandwidth usage.
Zombies has really not changed at all, in fact maps have been simplified, an extra game mode toward the game itself doesn't really succeed in adding even the slightest bit of juice to an otherwise over time boring game mode.
A game definitely not worth the money that's spent on it. And should be avoided.