I'm thinking Morrowind. In (q)HD. Everything set to max. Make it happen, Bethesda.
I don't think Diablo III would work thanks to their attitude of having to always be online all the time no matter what. That just doesn't fly well on a portable system. Even Phantasy Star Online 2 allows use over 3G.
Isn't the Ps3 version getting rid of always online requirement? That being said, I would have no real reason to get Skyrim on my vita, it would be so horribly watered down from my Pc version. Diablo, maybe didn't buy it yet mostly because of the stupid drm.