After two years on PS3 playing MW and MW2 I've bought this on PC. I'm appalled at how badly I'm doing! I used to swear by WASD and my trackball mouse but right now I'm swearing at the feckin controls! Never thought I'd be wanting a gamepad controller over a KB+Mouse!
Gameplay wise I'm enjoying it. It's a little annoying that you don't really start with any of the basic stuff (like a defib!) but I spent a few hours playing Rush as an attacker on an empty ranked server to unlock a couple of simple gizmos (mortars, health, ammo etc) then got bored so am back to be pwned by everyone again! I find the pace a bit more frantic compared to BF2 too but all in all I'm still finding myself saying "Just one more game" often enough!