Yes I know you pompous hipsters of video games will bash me for stating that but I have played this game for a week straight now and have come to an unbiased conclusion.
I haven't touched the single player at all because it's the same tired old hat that has been going on since Tom Clancy made Rainbow Six 1. I'm guessing this is why people bash the game. They don't want to shell out the money to access the multipayer. They would rather pirate the game for free and endure the awful singleplayer storyline until they put it down and never think of it again.
MW3 indeed shines in multiplayer. Yes it is plagued by hackers but %90 of the time they stick to team deathmatch where they can level up extremely fast. The fun starts in hardcore mode, which brings you back to the essence of counterstrike. No re spawning DE goodness. No hud at all. You can't see your crosshair unless you aim with the ironsight. You cant see how much bullets you have. FF on. If you shoot a friendly it doesn't kill them. Instead the bullets you shot simply bounce back and kill you. This negates the terrible troll tragedy that was never fixed in games like
http://www.moddb.com/mods/battle-grounds-2 Nothing other than a pointer telling you where the bomb sites are. Unlike counterstrike, the game tells you which site the bomb has been planted in so that you don't go through the trouble of running to the wrong damn site, which pissed me off to no end in counterstrike.
There's other fun hardcore modes like sabotage, which plays pretty much like football except everyone has lethal guns. Capture the flag, King of the hill, etc. People say it's almost exactly like black ops but I don't care because I never bothered buying black ops. As a seasoned gamer I know that companies make a decent game, find out all that's wrong with it, then make a sequel with all the glitches ironed out. This is exactly what happened with black ops and mw3.