MW3? You meant MW2 - v2.0, right?
Before I go into the bad, let me start by giving you what you might enjoy in this game. The single-player is what you expect a CoD game to be, great! However, at a measly game time of roughly 5 hours, the experience is short and hardly warrants a $60 price tag. The core gameplay is extremely close to MW2. For most players who played MW2, that's either good news or bad news. Good news being you'll hop on and feel right at home. Bad news, you won't be missing much if anything at all if you just pop in your old MW2 and play that. Most the perks and game modes CoD players are used to make their appearance in this installment with the introduction of a few new ones. A new game mode is Survival (similar to BO and WaW's zombies or Gears3' horde). The other is Team Defender which consists of you holding a neutral flag which doubles the points gain per kill if one of your team members has it.
So now you're probably asking me, "Wtf are you B*tching about?" Well, technically all you're getting out of your $60 is a few uncreative game modes, a few perks that been tweaked a bit, and 5 hours of campaign. The sound effects in this game is pretty bad. In BO I complained about how the guns sound like plastic toys. Well in MW3, they sound like miniature cannons and lasers. Not all, but some of them. The game provides you with almost nothing new or invigorating. The multiplayer maps are TINY, and most of the game modes are limited to 12 players or less. The maps are uninspired, and most of the time you feel like you're playing on the exact same map just different textures. If you're a fan of sniping, then best of luck to ya because you'll probably won't make it due to the size of the map and how easily a sprayer can outgun you.
So in conclusion, I personally do not recommend you buying this game, at least not at the price of $60. You are definitely not getting your money's worth. If you have to choose between BF3 and MW3, I recommend you BF3 mainly because the game delivers you more contents that'll give you the most bang for your buck. If I'm gonna get branded as a BF3 fanboy for saying so, then so be it. I like BF and CoD for the games that they are, but this year, I feel BF proved itself the superior product. As for MW3, I am GREATLY GREATLY disappointed.