Volume slider (vertical left side in the overview mode just above the settings button and somewhere in the cover art mode)
Airplay menu in overview mode (it can only be found in the full view (cover art mode))
Multi gestures (example: slide two fingers up or down for volume control)
To be able to search in a playlist
Double tap the fullscreen view flips up the artist overview
As you have choosed to use the leaf navigation (sliding pages sideways for the hierarchy) dim down the pages in the background so it does not get so messy as everything have the same light grey background color now.
Jump from song directly to Album
Improved pane navigation
Genres and Top Charts
Easy access to album and artist panes from Now Playing Menu (e.g. like in the desktop app where you click on the artist name)
Being able to "star" a whole album.
Swiping through cover arts in the Now Playing panes only starts playing a song when you *let go* of the swype, i.e. to allow you to skip over tracks easily.
I moved this over to the iOS board. The issue with multiple ideas in a single ideas post means that it's very hard to actually every say "Yes, this implemented". With an idea such as Gapless Playback, it's easy to state and prove that it's in place, while something like "Improved pane navigation" is rather vague. Some people might be happy with the current UI choices.
As a thread, it's a little easier to discuss what idea people all agree on - Then, they can create their own ideas thread for that idea, and we can gauge how popular that idea is. And then we can see about making that idea a reality. Hope this helps.