Even with the "killstreaks" they added, the MP feels nothing at all like COD. Just got off a four hour session with some friends , and they were comparing it to H2 mp. I didn't get to play H2 multi but i played a lot of 3. So for me it plays like a faster H3 with killstreaks. Also i'm not sure if the auto aim is gone or just really toned down compared to the last two games, but its a hell of a lot easier for me to line up a head shot now that my gun isn't following another enemy that happens to be nearby.
I enjoyed the campaign , it was gorgeous to look at with some great sci fi set pieces, i didn't care much for the final level though , but i really liked the ending. Very solid Halo campaign IMO.
Single player wise
CE>Reach>4>ODST>3>>>>2