I thought the campaign on Veteran difficulty was a bit too easy for me.
It was actually probably the easiest of the Veteran campaigns of the entire COD series and far easier than "Black Ops" and far easier than the nightmare that was "World At War". I also hate that some of the spec ops require two players as nobody I know plays this game.
Other than that, MW3 is among my favorites of the COD series. The other major problems I've had with the game is the constant hacked multiplayer games where there is too much camping and it being nearly impossible to score kills without just getting torn apart by cheaters or those using aimbots.