The problem with most of the people on this forum is they expect BF3 to be another COD game.
BF3 is not COD, doesn't play like COD, and if you go expecting that, you'll be disappointed.
I'll admit, the single player campaign blew hard. Multiplayer is a blast. And don't let all the glitches scare you away. It's glitches that make the game fun, especially when other people are there to laugh with you.
I like both BF3 and MW3. They have completely different kind of gameplay and it's mostly a matter of taste.
I started playing MW3 yesterday and the first things I thought about were that the menu's were exactly the same as MW2 and how bad the graphics looked (maybe I was spoiled by BF3 graphics). You do get the great fast paced CoD gameplay. Maps are extremely small. (Smaller than BO or at least it feels like that for me.) But BF3 has much better gameplay overall if you don't take preference and bugs/glitches in account. Killstreaks were cool 5 years ago but it's not enough anymore.
Maybe a lot of people expected something else and are disappointed. If you wanted MW2.5 from BF3 then you should have just waited a week for MW3 and keep playing CoD titles.
I'm still going to play tons of MW3 because it's a great game, like all CoD titles, and I just had 160 hours of BF3 behind me so a little diversity is nice.