Run blocking, the tackling system is greatly enhanced from 11,(no more horsecollar tackles, more tackling below the waist), DPP, hot and cold streaks, tighter zone and flat coverage from past versions. I didn't even add in much less suction tackling and blocking.
By the way, no game is without flaw and I haven't said that about Madden 12 is, either.
The animations are certainly better, but the results are still the same; an ungodly amount of broken tackles by the CPU, and something I even noticed playing multiplayer, as long as you juke / spin at the right time, you'll always break tackles.