BC2 is quite fun, has vehicles can width stand more players and blowing stuff up is fun. Walking around with a grenade launcher and blowing a hole through the wall killing 3 guys is always satisfying. The vehicles aren't cheap cause there is always ways to kill them quite quickly so your not getting spawn killed every time you spawn. Only downside for me is is that the sniper is a bit of a pain in the ass, for me that is.
Mw2 has its flaws but still manages to be extremely fun. I find its a bit more fast-paced but not by much, and the weapon choices aren't too shabby either. I find that everything you do in the game is apparently "Noobish". You get a grenade launcher and use it all the sudden your a noob, But really if they didn't think it was cheap and added it to the game, it's fair game. The perks are somewhat usless and most people use the same ones that actually effect the game play. Last thing, The nuke really does just sort of ruin the game.
I do like both Games and take what you will from this. I find myself play Mw2 more but thats only because my friends play it more.