To me, a multi-touch DS 2 is a no brainer. As are dual touch screens and at least PSP graphics. But I'm interested to see if we'll get dual analog or an alternative to help in movement. Some basic accelerometers wouldn't hurt, either.
# of games above 75 on Metacritic (including downloadable):
360: 241 DS: 144
PS3: 152 PSP: 126
Wii: 85