Been playing the game a lot since release...over 54 hrs, as of yesterday, but now my stats say 48 hrs, *shrug*.
I'd say it's a far better game than the first, and I really liked the first game.
I can't say I've found a problem with the controls, plays exactly the same to me. Maybe check to see if Mouse Filtering is off, or if any of the graphics settings are causing a bottleneck. I play with everything maxed at 1360x768, vsync on...no problems.
Really like the Realism/Expert mode. Much greater challenge and each kill is far more satisfying with Shotguns and Melee weapons seeming to be the best weapon options in this mode. As I don't try and cheat the game (see the majority of the "how to..." vids), haven't finished this mode...yet.