All hype, no delivery
First, the single player. The campaign is excellent, delivering exciting set-pieces and exhilarating combat. It greatly improves upon the previous games in the series, especially where AI is concerned. No longer do you have to push forward until you hit the magical barrier that stops the unlimited enemies respawning, and no longer do you have to manage being constantly hemmed in by grenades. On veteran, though, the game provides almost no challenge compared to other games in the series. It seems to get you ready for the multiplayer by letting you camp and take all the enemies down. Great campaign, though a bit easy.
The multiplayer. This is where the game is supposed to be the best of all time, the second coming of Christ. It is god-awful. Classes. Great idea, great in COD4, absolutely flawed in its execution. You have people running around with marathon (unlimited sprint), lightweight (move faster), and commando (increased knifing distance) just irritating the living hell out of you. But you can deal with them. Then you have the campers, just sitting there with a sniper. You are even encouraged to camp with killstreaks, more on that atrocity later. Getting a bit frustrated now. The last straw. The noob tubers. You have these guys running around with under-barrel grenade launchers and One Man Army (switch class at any time) just ruining the entire game for you. You spawn, instantly explode. Turn a corner, blown up before you can even see the guys. And then you have these "pros" who abuse the game's auto aim, quick scoping everyone and their mother. Killstreaks. Oh god killstreaks. They were fine in COD4 because there were only 3, but here there are killstreaks for every occasion. Someone might have joked over at Infinity Ward, hey guys, what about if you get 25 kills without dying, then you get to call in a nuke and automatically just end the game! Then they actually put it in. You know those semi-irritating choppers from COD4? Now you get to be the gunner in one, with enemies actually highlighted for you on your goddamned screen. This would normally require an 11 kill streak, but with the ingenious idea of Care Packages and Hardline (killstreaks 1 kill earlier), you can get it in 3! The whole game you just seem to be hemmed in by killstreak rewards. And if you suck at the game, you even get an advantage, in the form of death streaks! This game was built for the casual.
So overall
Pros:
Campaign
Set pieces
Lots of options
Cons:
Multiplayer as a whole
Community
Short Campaign