Let me just say that I don't ever play the actual single game, only the online multiplayer. So I can't comment on what the single game is like. My opinions will be based on the multiplayer.
I haven't played an awful lot at the time of writing this review, but from what I have played, I do think it's good. The maps are quite nice, ranging from the very small(like Nuketown), to larger(like Crisis). The gameplay is the same. They've added some different kill-streaks, including one I remember from World at War(the attack dogs). I do think the RC XD(remote car bomb) is quite fun for a kill-streak. Driving it around trying to find someone to blow up.
I will say that most of this game is good, except one new feature that has both it's pros and cons. The COD cash/point system. I actually don't mind this feature, it's new, different and interesting. Instead of unlocking new weapons as you gain levels, you now have to "buy" them with COD points. Weapons are unlocked as you level, but you actually need to purchase the weapons with the points(which you gain from playing online games). My only downside with this, is that pretty much everything needs to be "purchased". New weapons, even weapon attachments(like a suppressor, or grenade launcher) need to be purchased, perks(from what I remember, like Ghost, Sleight of hand) and Kill-streaks. Ok, this isn't a bad feature, and will take a bit of getting used to, but it is different and I would imagine that a few people may share the same feeling on the issue. Another bad thing about this is that if you buy a gun and don't like it, then it's points wasted. You can't try out the guns. Whereas with the old levelling system, if you used a gun and didn't like it, you didn't have to use it again and nothing was lost. Now, you try saving up points for a new gun that you think may be good, you buy it and it turns out pretty bad, you can't do anything. You've lost the points. Which can be a pain especially if you're trying to save up for something else as well. But, I don't know, I guess it's something to get used to.
So far, I am enjoying the game and am looking forward to really getting in to it.