Google Music

I find the "Instant Mix" feature doesn’t work so well for soundtracks as it does for strictly lyrical forms of music. For those of you who don’t know, Instant Mix will generate a playlist on the spot featuring other music from your library that supposedly shares the same attributes as determined from an algorithm.

Occasionally it’ll be consistent (like if you have two different recordings of the same song), but at times it’s hard to distinguish it from a random shuffle.