The list of niggly issues:
- Drag and drop - from the library/ filesystem-browser to the playlist
- The playlist table is very rigid. You cannot manually sort your tracks (say just dumping the tracks to the bottom of the list) or dragging tracks around the table.
- The progressbar does not allow 'click-to-position' interactions.
- The progressbar is in the wrong location. It should be in the status-bar area.
- The album-art retrieval is, although more efficient, less capable (the albumart.org searching api is pretty limited)
- No capability to remove tracks (from the DB) that have been removed from library directories when the application is not running.
If that lot doesn't take too long the list of features that may get a look at ( most easiest to do first):
- .m3u playlist read/write
- mass-storage device (Android phones, etc) read support
- mtp device read support
- ipod read support
In summary: issues and usability comes first. Features come last.