I came from Google Play Music (now YT Music) and the recommendation engine there was much better than Spotify. Spotify has pigeon-holed me and now all it recommends is jazz fusion and the occasional UK garage track. I do like to listen to those from time to time, but its recommendations tend to be oddly narrow. I just never feel like it's on the money, where GPM seemed to strike a good balance between new and familiar.
What bugs me the most is in any playlist of a genre I've listened to before, it seems to avoid adding new songs to the furthest extent possible. If I've liked a song by a given artist, it seems like I can be pretty sure to hear that song in every relevant playlist, but ONLY that song. Forever.
TL;DR I don't like Spotify's recommendations and aside from their terrible ethics in relation to musicians, it's one of the reasons I'm planning to switch to Tidal one of these days.