MW3 is easily the worst Call of Duty to date. The campaign is short (and story is absolutely terrible), multiplayer is more of the same, and the game's overall feel just seems like a slightly beefed up MW2. The original Modern Warfare had one of the best campaigns of any game and MW3 continues the trend of the very cheesy and ridiculous story that MW2 had.
It is very disappointing since the original Modern Warfare was so incredibly awesome. MW3 multiplayer is not even nearly as fun as the previous Black Ops. I played probably hundreds of hours of online Black Ops and couldn't get into MW3's at all.