I'm going to be somewhat cliché and say Black Ops II. I've enjoyed every Call of Duty release since Call of Duty 4: Modern Warfare, and I agree that in a lot of ways it has become very complicated in ways that only take away the value of the gameplay. Modern Warfare 2 is probably the earliest example of this, as a wide range of new kill streaks became available that made for some interesting (and sometimes frustrating) situations.
Nevertheless, I think Black Ops II has continued the trend in a responsible way. Developers had no choice to but to continuously add things. No one wants to change the moneymaking formula, and therefore they're left with three options: (a) Keep things the same, (b) take things away, or (c) add things into the mix. It's clear that options A and B are counterintuitive and would not create a solid formula for gaining revenue. We might look back at World at War respectfully now, but I can still remember the threads of people complaining that the games were identical in many respects aside from the change in historical setting.
Black Ops II has a lot of score streaks available, some immensely powerful, but a nice system of balance. It's fairly easy to take out just about any form of equipment or aerial attack if you have an EMP grenade or a proper rocket launcher, so even a player who racks up some awesome score streaks isn't going to be able to obliterate a well-prepared player. Also, they handled their changes to the way you create custom classes in a very good way. People often worried at the beginning that the ability to have four or more perks would create "super soldiers" that had an unfair advantage. This hasn't turned out to be the case whatsoever.
So yeah, Black Ops II all the way. Treyarch did it right with the exception of the game's servers and freezing issues.