I have always found the vast majority of recommendation engines to be completely underwhelming. There is one exception: Spotify. It doesn't seem to work for everybody, but personally, I get insanely good recommendations from Spotify to the point that it has become my main way of discovering new music (and discovering new music is very important to me).

What is the difference? On the surface, it doesn't seem like music recommendation should be a very different problem from movie recommendation.

Unrelated to this: I find the comparison between Netflix and Spotify interesting in general. Why do I get (pretty much) all the music there is on Spotify, but I cannot subscribe to a movie / tv streaming service that lets me access all the content for a flat fee? As a consumer, I would much rather have the choice between three well polished streaming platforms that all offer the same content compared to the current situation where you have a fractured catalogue on platforms of wildly varying technical quality (looking at you, Amazon..).