Stuff I left out:
1) Configuration. Frankly I don't care much about what the options/config UI looks like. I'll rarely use it, and when I do I'll be parked, and I might even have my keyboard out. Desktop-like UI would be fine.
2) Playlist management. It would be good to have a way to remove the current song from the current playlist. It would be good to have a way to add the current song to any playlist. Those buttons might go on the main screen (but smaller than the buttons that lead to the major features) or perhaps on the main 'media' screen. I don't feel strongly either way. (In fact I'd be OK with not having them at all, though I realize I might be in the minority there.)