From a game design perspective BF3 is disastrous.
They added some awful mechanics--lasers and tactical flashlights being the worst. Both will blind you if an enemy points them at you; problem is, this also works if an ally points it at you, AND will work if an ally is simply running around with the light on, since the running animation dictates that at some point, the light will point at you. It's extremely frustrating and is absolutely awful on the eyes.
The map design is really bad as well. There are three or four conquest maps plagued with tunnel syndrome, where the middle capture flag is just a huge choke point (usually a tunnel, lol) that causes players to camp on each side and fire rockets and grenades at the other side. There's no action whatsoever on these maps, and anyone that tries to push the pace just gets mowed down.
DICE really played up the whole progression system when they marketed the game, and it's awful. They did it Black Ops style, with each gun having its own set of unlocks. Problem is, this isn't Black Ops, and each side has their own set of starting guns. So if I unlock something for my Assault class rifle on the Russian side, I don't have that unlock when I play on the American side. It's stupid, it's trite, and it forces you to grind everything out.
Low point of the game for me: shooting the back of a Growler IFV (it's basically a Jeep with a gun on it) with a RPG-7 from 10 feet away, and not destroying it... only disabled it. The guy mounted on the back then turned and killed me.
High point of the game for me: watching two enemy jets do a somersault in an attempt to catch an allied jet, only to collide mid-air and explode.
7/10 from me. Great graphics, superb engine, and it's the first game that's ever made me say "wow" out loud, but the core game is just fucking awful. I enjoyed BF2 and BFBC2, but this is just a huge step back in terms of design.