CoD really sucks now. The fanboys ruined it, now all kids think they know guns and they think they can just walk to an army base and grab a barrett and go to iraq and kill all the insurgeons. The worst part is it makes a joke out of war, you get shot once, big deal, you wait for the red to go away and you can keep going, in real life you'd be screaming for a medic on the ground and have to get airlifted out and maybe even die, and you can win a fight over an urban street in about 5 seconds, war takes a long time realistically. And most of all, you can just respawn if you die.
but the realism aside (cause most games are like that, even the ones I like), CoD stole most of their entire game setup from Counterstrike.
But that's just my opinion, CoD4 was the last one I bought, and I'll probably sell it. Rainbow Six, or any Tom Clancy game is so much better because Tom Clancy knows what the hell he's talking about and has studied warfare very thoroughly for a long time and writes some pretty good books about it.
/long ass post