I was playing MW2 online and i m hugly disappointed.I only played a bit of online from MW1 and WOW and for this one i got upto level 10 .

let me start:

first of all the maps are too big for 10 -12 people.

I agree. A few of them are too big. However, I felt the same way about Killzone 2. 32 person online didn't feel any different than 12 person online because of the expansiveness of the maps. It took forever for me to spawn after a death and get back into the battle. I end up with roughly the same proportion of kills/deaths in either game, so I must not be seeing more action in one more than the other.

graphics online is like a polished PS2 game(SP is beautiful but online ,,,ughhh)everything is low res it's like rainbow six vegas graphics .

You're either blind or you're semi-blind and playing this on an SDTV. MW2 isn't the most technically impressive game ever, but it is no PS2 game.

the minute you step out your dead from an unkown place.

Sucks for you. Go check the Killcam next time and it won't be an unknown place you get shot from anymore.

it's very fast paced like UT3/R2.

I don't know about R2, but it's nowhere near as fast as UT3. You must go back and play UT3 so you can realize how wrong you are. MW2 is definitely faster than Killzone 2, but KZ2 also happens to be quite possibly the most purposely slow FPS in existence. 

Class based multiplayer with different ability is much much more fun.

Not sure what game you played, but there are a multitude of abilities in MW2. It's called Perks and Killstreaks. Regarding classes, that's fine. That's your opinion.

the only positive is that the aiming system is extremly forgiving of your error while shooting.

I honestly don't see why this is popular at all.

KZ2 is much more epic and hectic with 32 players in the room.with 10 turret bots,8 air support,etc...

I give MW2 online a 6.5 and a 9 to KZ2 online.

people that are even comparing the graphics of MW2 and KZ2 either are joking or haven't experienced KZ2 online.