I bought BF3 a couple of days ago because I fancied a change. My thoughts so far after playing purely on multiplayer:
Negatives:
There should be a way to back out of a lobby between games. Seriously annoying.
The graphics on MW3 are better imo. Everything on BF3 just looks a bit crappy to me.
When people jump over walls or something they fly like 10 yards past it. I keep having trouble climbing through windows and stuff. It just randomly doesn't work sometimes and I'll be stood there jumping up and down on the spot like a tard. Movement on CoD is always so smooth and easy.
Would be nice if there were more game mode types.
Guns don't seem very accurate. I fire in short bursts but sometimes it'll just keep missing even if I'm aiming right at someone. It seems much worse when the target is prone.
Servers don't seem too great. I've seen more lag on BF3 in the past 2 days than I've seen on MW3 in weeks.
Positives:
Rush mode is epic. The maps are immense, so there are loads of different tactics to use on every game. Each set of M-COM stations will require a different strategy to attack/defend which makes every game interesting. On MW3 you'll only really use one class per match.
The class system is pretty damn good. Being able to change your class completely during a game is excellent. So if you're using the recon class but the gun isn't working out for you, you can just change the gun without switching class. This makes for great flexibility.
I didn't think I would, but I like the emphasis on score > K/D. You can be an asset to your team without getting 20 kills and no deaths.
Conclusion:
I think MW3 is a much slicker product. BF3 could've been an absolutely amazing game, but there are a few sloppy touches which I think detract from it. There is no doubt that it is a far more challenging game than MW3, but that doesn't necessarily make it more fun. MW3 you can pick up and play far more easily, which makes it more accessible for more people, which in turn makes it less challenging for those who are experienced with FPS games.
Having said that, I'm enjoying it immensely so far. It is nice to play an FPS where tactics and teamwork are more important than trigger-spamming. And I don't ever die to dual-wielded SMG faggots who can't aim properly.
Highlight so far: Holding a corridor single-handedly using a sniper rifle on the subway map against waves of attackers. Ended the match 21 for 3 with a killstreak of 14