I got it last night and I'm really not impressed at all with MP. I played it for about 5 minutes and quit. Nothing about it was fun for me. However I like the SP engine and if it was used for MP I would definitely play it.
The biggest annoyance is a lot of features in SP are not in MP like lean, prone, sprint strafe (very big annoyance for me), to name a few. Why they used such a limited engine for MP is beyond me because it ruins the game.
Looks like I will play through SP and never touch it again. Bring on Black Ops in Nov.