I'm guilty, I liked it.
While playing the singleplayer mode of this game, I didn't understand what was all the fuss about, an average shooter with nice graphics, wide variety of weapons, and good storyline, but other than that, I felt like Modern Warfare's Singleplayer experience was just too plain simple. I shot that guy ,threw a grenade there, hid behind cover to heal myself, and basically that's it. The singleplayer for Modern Warfare 2 was not as fun as I imagined, and yet people got so excited about this game, which did not really come up with a new mechanic or idea.
So after I finished the singleplayer I went online, thinking "What difference is there?" and there was plenty.
The moment I went online I knew this game wasn't as bad as I thought, it doesn't require too much of a skill like in Counter strike or Team fortress to really score some kills with a sniper rifle, and it's pretty user friendly and not as terrifying as, for example, starting a new class at World of Warcraft- When you start playing online, you know what you're doing, and in case you don't, the killcam mostly shows you where did you go wrong, so that the moment you get back on, you know how to get your payback. The gameplay online is absoulutely thrilling, the satisfaction you get from shooting down an opponent, earning a reward, or just securing an objective is plain fun, in fact, it's so much fun that even when you're taken down several times, you have this urge of trying to get back at your rivals, showing them you too can kick butt.
I must say that Modern Warfare 2 perhaps didn't create a new way of playing, but the reward system was so satisfying you could say it makes the game, it gets you to want to play not just for the excitment of winning and defeating your opposing team, but for the sake of unlocking, and it feels more than great to recieve a new weapon or attachment knowing you achieved that by doing your best.