Honestly, I don't get why everyone's rating this game so harsh.
Now, on that note. I have to say the multiplayer is much refined in this installment of the Modern Warfare series. I no longer find myself dying every six seconds from a grenade launchers (cough, cough, Modern Warfare 2.). Perks are much more balanced now, as well as the guns, for the most part. I really like the fact that you can level up your weapons as well. If you like a gun and use it constantly, you are rewarded with things like reduced kick or less sway, which comes in handy. The killstreaks aren't anything new really, but those too have been balanced out better.
Singleplayer is exactly what you'd expect from the MW3 franchise. Full fledged firefights and cinematic moments are ever present throughout the game. And, in an attempt to not spoil the campaign, I will only say this- expect major plot twists.
One complaint I have is with the customization. Or rather, the lack of it. I wish that Modern Warfare 3 could have included better customization, such as how your character looks. And I don't know if it's just me, but I've been having trouble with connecting to servers a lot of the time.
Overall, MW3 is a good game. Yes, it isn't exactly the most original. And it looks and feels like it's predecessor. But, it does bring some new things to the table in the way of multiplayer, and with a strong campaign, it's actually a very good game.
8/10