For those who are just looking for core gameplay chances, improved Hell in a Cell and Cage mechanics, as well as this Payback perk system appear to be the biggest changes. Payback is essential another category of assignable skills. But these appear to be a little more drastic.
You have one that lets you auto reversal the next incoming move as long as you're holding the button down, one for an instant finisher, one that lets you play possum, etc. Others for cheating moves such as low blows, poison mist and brass knucks.
Aside from that it seems largely the same. New OMGs and little animations here and there as usual.