I think I like the addition of a few new aspects (climbing with picks, hart beat monitor on one of the weapons, new weapons, etc.) to enhance the game play a bit more. I also felt the detail was pretty amazing, in particular the fast food restaurant shoot out and the D.C. part of the game. The MP actually ran a little smoother, (or as smooth as the first Modern Warfare) than MP WaW ever did for me. Even when I boosted the graphics card, added more memory and turned down all the in game graphics (which is unfortunate). With pings in the 50-60 range WaW was always laggy for me, which is why I continue to get the best results with CoD2 (and the GBI server in particular). Don't get me wrong, for me, the MP MW2 is a bit frustrating at first, stuck with NOTHING in the beginning against players who have EVERYTHING. To be honest, I never really played WaW or MW1 / 2 enough online to make a good evaluation.
Guess I'll stick with the tried and true......