I'd like to know more about the new facegen system. In Oblivion, I was frequently irritated by the fact that changing the width of someone's nostrils could alter the shape of their eyes and that changing one control in the Tone section could suddenly turn your 19-year-old character into an old guy. Control over asymmetry would also be great. If these issues are fixed in Skyrim, there will be no end to my jubilation. I'm already really happy about the increased customization on the generation system in general, though.
A disguise system would be cool if it works properly, but I'm more interested in the practicalities of crime. If you kill a guard, will everyone in the entirety of Tamriel know about it instantly? Can you bribe or blackmail or threaten them?