A bit of a tangent, but I liked the Rdio model where you could configure how "close" did you want music suggestions to be. Sometimes when I play a band I want to only listen to their music and some very similar music, othertimes I want to discover something different.

Another great functionality is what Last.fm had way back in the 2003-2004 where you could input 2 or 3 different artists and it will generate a "radio" playlist of music similar to them. The closest thing I've found so far is https://www.gnoosic.com/, alas, they don't generate a playlist.