I can only speak from online multiplayer, but here is my review.
This games is not as bad as people are making out. This game has been relased with a lag issue that is affecting all online users, so other then the lag which will be fixed, I cant overly fault the game.
Server management is far better on the PC compared with MW2. You have dedicated servers and you can see where they are based, what they are running (map, game type etc.. ) and the relative ping.
A lot of MW2 plays may not like this, the maps seem to have been designed for fast game play. There are camping spots, but no so many as MW2.
The advancing in the game is different. Takes a little getting used to but is the main thing that sets this game from MW2.
Customisation is a little disapointing. You can customise the face and logo's. What I want to see is a real choice of cloths rather then being forced into wareing what your skills make you.
Nice selection of weapons/attachments.
Only 50 levels that ive seen so far and 15 prestige.
Once the lag issue is fixed, I would put this on par with MW2. Just because MW2 server management is the worst i have seen on the PC.