No customizable sections to sort the library
It's an issue many music players face all in the light of trying to be sleek and modern: no customizable sections to sort your music. While actually this makes them feel more limited and clunky. Right now I have for example no option to browse all tracks present in my library, but I do have a lot of sections I never use (luckily there is at least the option to hide those).
If it'd be possible to add and remove your own filter options based on custom ID3 tags - complete with an option to set a title for this new section and icon - it'd be the perfect music player for me.