Well here goes:
Single player was short, but decent. Ignore the story because its only purpose is to connect point A to point B, and you have an alright game.
Spec Ops takes a little effort, and you MUST play with a friend(because alone just isn't as fun), but overall, I like it. It also provides a good challenge if you try to beat the IW best times.
Multiplayer is pretty good too. Now that they've fixed most of the major glitches, I can't say that I have a problem with it. The main thing that I see is that it can punish you tremendously for trying to run around like an idiot and for trying to be a good sniper. It all depends on who you play with. Not your weapons or levels or perks, but the people you play with. All guns kill enemies, you just have to shoot them. All levels provide for decent gameplay, you just have to learn how to navigate them. And the only purpose of perks is to enhance your style of play, which you must discover on your own.
The real con to multiplayer are the people who complain about camping, tubing, knifing, and using models. A so-called camper is a player who isn't stupid enough to run into enemy fire in hopes of getting a kill. Those who complain about campers are the ones who keep running into that same spot and dying. If grenades are an issue, use a blast shield. It was put there for a reason. Don't like knives? Heart-beat sensor and learning to look in directions your teamates are not. And finally, having shotgun troubles? Treat them like stabbers, and then find a good sniping point(ie 'camping').
Main point: It can be fun if you want to play with a little thought and patience. If you try to go all Halo and regenerate your way through combat, you will die.
[sub]now where did I put that flameshield picture..[/sub]