The main reason I like MW2 is because its one of those games MOST of the people on my friends list own, so it makes it an easy game to get a good group of people I know playing. It gets less stale when you aren't playing with a bunch of idiots who for some reason think the voice chat feature of the game entitles them to do their american idol auditions to everyone else playing. (that and the high pitched 9 year olds who think its cool they know a few curse words).
I set my mic to friends list only for this very reason. I tried playing with it on, but pub matches never are one for much teamwork. Just the aforementioned 12 year olds acting like a hard ass. I think my main problem with it is the past 20 or so games I've played (mainly domination) people never went for objectives. It's one thing to capture and defend, but when you just run out of the gate to get to your favorite camping ground, and ignore even getting the first flag, it makes for a frustrating match. To top it off if no one helps you get flags you'll spend more time getting blasted then you will earning points.

I do enjoy playing with my friends still and if I hop on and a bunch of them are in a party, I'll most likely join. I still like the game, I just wish the pub matches were better. There's not much I feel is unbalanced in the game (save for two perks), but it's really hit the point where they need to release some new maps.

Oh, and that stupid care package glitch was crazy annoying when it was unpatched. You couldn't play a single game without someone ruining it at the end with never ending harrier strikes and chopper gunners.