The game is great and all, but anyone coming from a difficult FPS game (not CoD4) like CS:S or BF2 will have a breeze.
The singleplayer game involves many things one cannot normally do in multiplayer, such as ice wall climbing, etc. Anyone who played the last game should be very clear on what to expect from this one single player wise.
The multiplayer, from what I have noticed, has changed quite a bit. I had CoD 4 on PC, and honestly didn't like it that much. I now got COD: MW2 for Xbox and love it. The only problem I have with the multiplayer is that there are a few perks that really should be thrown away completely.
For example, I hate the airplane and helicopter perks. They are basically giving the other player the ability to kill you instantly with this way overpowered gun, and the gun shoots through a lot of material. If you are outside and anywhere near this thing, you die. I would much rather have none of that, and just more Player vs. Player. Honestly, I can't tell you the number of times I have died because helicopters hunt me down, and unless their time limit runs out you have to shoot it down.
Also, multiplayer is shockingly easy. I won't blame the game for this, but I literally got the game in the mail today and I am already at the top or 2nd at the end of each game. Anyone with experience in CS:S will tear this up, because CS:S is just a much more difficult challenge. Same thing with BF2. I am not saying that it being easier is worse, just saying that it really is not difficult to be good. It usually takes me a few weeks to get used to the feel of the new games and become one of the better players. Here it seemed to come very easily.
Overall, I am clearly recommending this game to any console owners only. PC gamers should want to be able to choose which channel they want to join, but for consoles this process of being thrown into matches automatically makes everything much easier.