I'm not necessarily saying MW3 is bad, but it's more like MW2.5. Graphics not that different. Gameplay seems to be more fine tuned as opposed to completely new features introduced. And it is ridiculously overrated.
Well I never bought MW2, I always just played aIW. I haven't gotten bored of MW3, at all, yet. Survival is fucking amazing, I could play that for hours without end. The multiplayer game play is fucking exhilarating along with special ops and campaign. $60 well spent.