My problem with all music recommendation engines, and for many intellectual music aficionados, the lyrics content - what is being verbally described in the music - is what I seek and hang on for my preferred music. When I listen to my collection, the genres are all over and I don't even know them. I listen to the words and treat the music as emphasis for the words. I'll have ska, 30's jazz, hip hip, and classic rock all in the same mix and it works because the lyric content is different takes on the same things. In fact, new friends are sometimes dizzy from my music choices, and then at some point they hear the thematic concept of my mixes and get it.