The aim assist for PC is bullshit, and I kinda agree about the graphics. MW2 had a much richer palette despite the fact that it's still a "realistic" looking game.
Can't really blame it otherwise, it looks ok to me, even if it's not cutting edge (and it also means it's more accessible to lower end rigs. I find it appalling that BF3 runs like shit on my PC on the lowest settings, but I can play MW3 on max, no prob. And no, BF3 doesn't look THAT much better).
Not exactly certain where that fps cap was, I played it at over 60fps on a gaming laptop, and the guys that configured them barely knew how to start the game, let alone change config files.
I've found balancing to be an issue in all MW games and I really haven't played enough of MW3 to comment on it further, but at least the weapons no longer seem to be futuristic laser guns wielded by immovable cyborgs since they seem to be perfectly accurate at any range with no recoil whatsoever (I'm talking about the assault rifles in MW2).
And yeah, the weapon unlock system is kinda shit too... I know it gives people a feel of achievement, but at least give us all the weapon accessories. I refuse to play without a red dot sight!
In the end, I also find MW1 to be the best game of the series, not only in MP but also in SP. The balance is ok (as long as you restrict the usage of the GL), weapons feel different and take actual SKILL and MASTERY to use properly (you know... stuff like learning to control recoil, accuracy, reload times, etc), killstreaks are powerful, but they can be neutralized/avoided by a skilled team/player (hear that AC130?) and the maps allow for a greater degree of tactical play.