Most people will pick Modern Warfare 2 because it has better graphics, and better gameplay maybe? I've only played CoD4 on the PC, and it's not as fun as a console for me :/.
well if you look at it this way. cod4 was alot better at the time. there was nothing like cod4 one of the biggest games ever to come out in the history of games game informer gave it the number 4 game of all time. and i believe that mw2 didnt live up to its massive hype. i mean dont get me wrong im playing mw2 right now but it will never live up to what cod4 made of the modern warfare series. i mean come on... uncharted 2 is better the mw2