What has changed is not necessarily much. The gameplay is the same as in MW2 or Blackops. A campaign which is played out by more than 6 hours and Multiplayer Fun at its finest. Fun it all, just log in and bit off steam without great transitions DRM lungs.
However, I have to deduct a star, because I would have liked a bit more innovation. The well-known principle of Modern Warfare's just sucking out so slowly.