Just finished the single player, great campaign overall (much better than Black Ops which was awful imo). I still find the actual shooting enemies parts to be dreadfully boring though. When you get up to some square area and there's tons of enemies coming from various buildings etc, these are the worst parts of the game for me by far. My favorite parts are when you're just following an AI guy and you have to be quiet, pass other guys, and so on.
The parts where you're running with
and the music is playing in the background as the rain pours down and buildings get blown up before you etc. is really awesome. But then they force you to stop and shoot 30 random baddies -_- kills the momentum for me.