Think i like about CoD4 is the way they actually make you need the use of tactics in the sort of way you have to use your brain instead of muscle attitude, that made a diffrence for me from the old CoD games to this one.
As an old military soldier, i was trained in street combat, and house searches, and by actually using the tactics ive learned, they people around me work the same way, and i can easily read what their next move will be, and that gives a more realistic feel to it. So i like the game in total, with the grafics, feel of "i wanna freaking nail that bastard to the wall". You want to fight, and that urges makes a game feel good to play, to give you that kick!:P