THE GAMES COMMUNITY SUCKS
Right there is the main reason why MW2 isn't great, the community. It's mostly comprised of:
Showboating Asshats(trickshooters, 360 noobtube/noscope/throwingknife[because most of the time these MISS])
Morons (Modders, Kill hunters[goes for kills only, when most of the time there's an objective to do])
and then that small sliver of good players that actually know what the hell there doing (Defend/Attack Objectives, Teamwork)
Seriously don't blame the game, blame the idiots who can't play the game.