The yearly release of a game within a franchise or series, in my opinion, is more than bound to end up boring the consumer base after a few years (sports games can get away with it best, but some loyal fans still skip a year or two now and again), and I believe Call of Duty is reaching that point, especially by dividing the fanbase with certain concepts.
I, for one, am not thrilled with the futuristic settings in the last few releases. That said, I believe Black Ops 2 held up well enough (and had amazing Zombies DLC) and actually am of the opinion that Advanced Warfare has been one of the greatest titles in the series (although I loathed the fact they didn't include even a single zombies map with the core game), but definitely saw Ghosts as the worst release in the series so far... by far. And frankly, it seems to me Black Ops 3 might give Ghosts a run for its money. I hope I'll be shut up in a month's time, but I can't say I'm looking forward to it at all.