I'm particularly excited for the new class. Honestly, I wasn't too much of a fan of any of the current classes as a previous Paladin player in D2. Should be cool.
As a lot of people have already said, everything! Class changes the most though. It's nice to see a lot of new stuff going into RoS and not just a few things here and there. Really hope I can get into BETA. The only BETA I ever got was WoW:MoP
I am really excited for the new act in RoS. All the information disclosed about Wesmarch makes me want to play it already, back to the gothic roots of previous games. too bad that we still have to wait at least 6 months.
Class balancing hopefully. So sick of my barb!
Regardless, keep up the good work!