I dont even play this game anymore...i prefer msn over it any day..

I enjoy it, only because I know how to have fun. The key is to not take the game seriously, only then can one find true happiness in MW2.

Here is the list:
Bullet Registration
Hitboxes that trail and are too large
aim assist that is too strong
anti lag that is too strong
matchmaking average ping is 80-100ms
host selection was unintelligent
commando
oma
shotgun secondary
machine pistols
customizable killstreaks that promote killstreak whoring
too many accessible areas on the maps providing locations for people to camp their killstreaks
not enough flanking routes in the maps
quickscopers (auto aim)
grenade launchers
silencers that didnt work
iron sites that were off center
getting shot around corners (lag + trailing hitboxes)
lack of recoil of weapons
lack of sway for weapons

I will stop there for now.

What made MW2 bad is commando making you invincible to bullets.

Infinite tubes is a problem although it doesnt really affect me at all. Dont encounter tubers too often.

I also think everyones health is too low. It shouldnt be as easy to kill/die as it is. Give the guns more ammo and make a kill take more bullets.

@DropDragon, those are all things people have problems with but they arent legitimate problems.