Simply put, this game is overrated, broken, and frustrating.
Before getting into the multiplayer, I started with the campaign, as I do for every game. I'm not going to reveal anything about it, all I'm going to say is that it doesn't make any sense at all and is really easy, even on the hardest difficulty available.
Audio/Visual: The graphics are okay, but they aren't great either. Up close, things start to become blurry looking. The sounds are worse. The guns don't sound realistic at all, some of them (like the M4 Carbine) literally sound like they are "squeaking."
Multiplayer: I've heard many people say that Modern Warfare 2 has the "greatest multiplayer ever." I have to disagree. The spawns are just plain terrible. If the opposing team manages to get a Harrier, Pave Low, AC-130, or some other killstreak, prepare to be spawn killed over and over again. I know that many, if not all, first person shooters have spawn killing, but this game, by far, has the worst spawning system. Apparently modding, cheating, and glitching is okay to do in this game, seeing as you can get into a match where every gun is automatic, the other team can see through walls, and knifing across the map is possible. I have been in numerous modded games myself, and they are not fun at all. Honestly? I fail to see how this game's multiplayer is as good as everyone says it is.
If you are looking at getting this game, I strongly suggest that you just rent it first.