It all depends on how you look at it. As a sequel to MW2, its great! As a sequel to Black Ops, nothing's changed.

User Rating: 8.5 | Call of Duty: Modern Warfare 3 X360
The game is not great, but its not revolutionary. The Spec Ops is fun, the multiplayer is immersive and the single player, although full of the cliches you have begun to expect from the CoD series, and although short, is full of action set-pieces that have defined the series. Like others have said, if it aint broke, dont fix it! I especially like the prestige shop and elite in CoD, the kill confirmed mode in MP is not so great, stick to the big'ol ground wars, domination and TDMs. Private game modes however are amazing - especially infecction. And *SPOILER ALERT* the nuke is back. Its called the MOAB (mother of all bombs) which kills all the enemies, which then respawn. It doesnt end the game. I think that MW3 is a definitive addition to the series and is something you should check out. P.S. I have BF3 as well, and Im being very unbiased here.
+ Multiplayer
+ Spec Ops
- Single Player
= 8.5