I've heard IW's was pretty good, I've played them all except that one. I really wouldn't call any of the others great though. Acceptable, with some fun shooting, but pretty poor design that just pales in comparison to games like Wolfenstein or Doom.
I know it's opinion and all, I just wish COD campaigns had some kind of hook to them other than what they have. Everything about them is just average. I did like AWs gameplay, as it did experiment some and the dash rigs made jumping around tons of fun, but the levels and story (like most CODs) were so bog standard that it hurt.