BFBC2 was my first BF game and I hated it at first because of the ungodly amount of rounds it took to kill someone and the fact that if one guy spots you the entire enemy team will light you up like the Fourth of July! Even when you are behind cover and they cant see anything but that damn orange triangle.
Thankfully Hardcore solves most of this. One shot kills, no wallhack spotting, no kill or deathcam, no magical crosshairs, and if your idiot teammate shoots you or lobs a grenade into your lap, it hurts!
The other things that really bugged me about BC2 were: I couldnt strafe, go prone, or lean. I thought to myself "How can a modern FPS not have the ability to strafe!". I have adjusted to it but that should not have to be the case. Blast you Dice, let me strafe!
That was the first thing I noticed when playing the BF3 alpha, the player movements that included the ability to strafe and go prone. It was so smooth and fluid and..... dare I say it? "Call of Duty like".