Just got out of my first couple games. Here are my first impressions:
First, I'm actually surprised that TTK is the major complaint in this thread, because I don't think it's that egregious. My biggest issue with the game is that it just doesn't feel good to play. It's as if, in the process of copying Black Ops 3, they forgot to keep the things about Black Ops 3 that mattered most, like the way the game felt and moved, or the intentional movement-based map design, or even the satisfying "pop" when you hit someone. The game just feels off.
As others have been saying here, it's like they took the core gameplay "feel" of Ghosts, and added Black Ops 3's movement system and specialists. But the core Ghosts part of it is what really destroys the game for me. Ghosts did not feel good to play. IW feels largely the same and suffers for it.
Then there's the more minor issues, like the bland menus, the unimpressive presentation of the whole thing. It's just a step down from BO3 in every conceivable way, and it doesn't do anything on its own to set itself apart. Advanced Warfare, even though it had its issues, did something different and I admire Sledgehammer for doing it. Black Ops 3 was genuinely different from AW and changed up the movement and multiplayer systems enough to set itself apart. But IW is aiming to be exactly like Black Ops 3 and it shows. It just doesn't click together; it feels like an imitation of a game rather than a game unto itself, if that makes any sense.
I'm a bit disappointed by it, but honestly not that surprised. I knew MWR would be the superior part of this game, and IMO the price was worth it to be able to play Cod4 multiplayer again. And who knows, maybe the IW campaign will be good. But the multiplayer is not a great first impression!