(I haven't found out how playlists work)
I'm missing a playlists "Recently added" (to library), "(not) recently played" and "(not) frequently played" (and similar)
Having "smart playlists" (dynamically updated result of a saved search) would be nice, also.
Having some whitelist/blacklist mechanism (Like / Don't like) to tag the current song would be great. So if you play an album next time those "don't like" would be skipped.
(Unsure what to do with the liked ones...)