I actually quite liked all the CoD games up to MW2 (i haven't played any others). The first 2 (CoD and Big Red One) were by far the best, but the others were good for there own reasons.
MW was nice, had good voice acting and mechanics, good graphics and original story. The only thing I didn't like was parts of the game where endless waves of troop shot at you from well defended positions. WAW had the zombies feature, which was a great idea in itself and basically made the game. I didn't like the campaign in it however, as it was just a rerun of all the other WWII games. MW2 was also really fun, the campaign was great with a nice story and cool cutscenes, the mechanics were fluid and easy. It was a lot better then MW and is probably one of my favorite console shooters.
I haven't played beyond mw2 so i can't talk for anything else.