I have recently bought this game and have 8-9 hours of multiplayer game time. I can't comment on the campaign as I only did the first mission then went straight to multiplayer.
My initial thoughts on multiplayer were very negative, I found the aiming ridiculous, I just couldn't find the right sensitivity, there just didn't seem to be that middle ground, it was either too high or way too slow. I was thinking i had made a big mistake with this purchase, but I really wanted to like this game (I LOVED bad company 2) so I kept playing. After a couple more hours I really started enjoying it, I was dying a lot, but I was just focusing on supplying team mates with ammo or medic packs and I gained a lot of experience points which lead to unlocking attachments for weapons.
Since unlocking those attachment it has made the aiming better, I have adapted to the style of the game, TEAM WORK! I am finishing each game with a positive K/D and a lot of points. That's the thing I love most about BF3, the fact that you can get points from anything! suppressive fire, kill assist, capturing objectives, destroying vehicles, defending objectives, reviving team mates, resupplying team mates, the game just rewards you for everything!.
I give the multiplayer 9/10, it really does feel like what I imagine a battlefield to be like :)