What annoys me about the CoD series is that the guns feel weak as hell. I know, maybe not everyone agrees with me, but they just feel and sound like pea shooters. Now I know in real life guns don't take heads and limbs off and insta-gib if you put a 9mm slug in someone's leg, no, it's just the feel of shooting and loading them, has no weight or recoil. I think even Counter-strike 1.6 guns had a better feel to them (anyone remember zooming in the Sig 552, that slow chunky crack you get instead of full-burst? And the silenced M4? Even the USP? yummy)
I also don't like over-the-top cheesy tough guy stuff, didn't mind it so much when I was young, but GOW 2 and Bulletstorm just made me cringe, many times. And I couldn't get more than an hour through Army of Two because of that fact alone. I think I turned the console off when you do that synchronized sniping bit, and pull the trigger at the same time. And then they do this corny hand-slapping bullshit.
Maybe not entirely relevant as a "hate" as I still play and finish lots of CoD games, and GOW2 and Bulletstorm.