Alright, I'm not going to be one of the ones that says "OMG this is the best game ever", because when thinking about it, how can there be a best game ever when there's still thousands of video games to be made? 
To start, campaign. I won't give any spoilers, so don't be cautious. It's all cool. The AI in this game is much better than in previous CoD games. Now in this they actually do something and not stand around and wait for you. The campaign is sadly very short, but it is definitely satisfying.
Multiplayer, what can be said about it. It's the traditional CoD multiplayer experience but with some tweaks to make it even better. I've only played Team Deathmatch so far, so that is all I can give insight to. In those matches, score limits are raised to 7500 instead of 750. Therefore, every kill you get, you receive 100 exp. There are many more weapon challenges which add much fun. The perks are pretty straightforward, not much of a change there.
Spec Ops is the big new addition to this game. And it's pretty much a combination of everything that has been the latest and greatest in video games. It has its own type of horde/nazi zombies that only goes on for a max of 5 rounds (or atleast what I've encountered). There are some scenarios that make reference to the levels in CoD:4. This is a very interesting addition to the game. There's defusing bombs, snatching intel, extracting to points, and much more.
Hope you all enjoy this game when it comes out on the 10th! 