My first impressions for the new Activision game are very good in general.
Campaign: The campaign is so intense. You continue the campaign where you left it in MW2. Soap is nearly saved when Makarov finally kills it. Price in revenge kills Makarov as well. But in general it's so good. I really love how Infinity Ward has developed this game.
Spec Ops: Spec Ops are also intense. There are two missions related to The Pit and some missions related with another points of view of the Campaign missions.
Survival Mode is also good. You have so much maps, divided in groups of 4. The first group is easy, the next are more difficult and so then, the last map is the hardest map in the game.
Multiplayer: I haven't tried the MP yet, but as far as I have seen it looks very good. Weapon Proficiency is great against camping.