I feel those are how Pandora and Last.fm (used to?) work respectively. Nowadays everything seems to just put a bunch of tags on a track and suggest you things with the same tags to the tracks you liked. Doesn't even need to match the same combination of tags, just some number of them. The problem is, you probably care about the small, specific tags, and the system cares about wide "popular" tags. If you like a couple niche genre covers of songs that happen to be featured in TV openings/OSTs, you are not getting more songs in that genre - you are getting a bunch of covers and OSTs.
I wish I had a music recommendation service built on Pandora's immense dataset of music tags that could build me a playlist that I could link back to whichever music service I happen to be using at the time. I could have it do things like require at least 3 tags in common between adjacent tracks such that it could jump around between 2 dozen genres but the transaction between any 2 given tracks isn't too jarring. It'd also be nice if I could tell it to make a playlist where every song shares one particular tag in common.
Maybe I'll build that. Sure would be nice to have.
The primary advantage of Pandora's algorithm is the human-labelled Music Genome database. I haven't seen any other company do music discovery as well as Pandora, and don't expect that to change any time soon.
