I found them to be pretty bad. Let's say I listen to genre X exclusively for two weeks, and then for genres Y and Z during week 3. The genres are completely different (lets say X - rap, Y - kpop, Z - just pop music). On week 4, I'd expect to be recommended a mix of X, Y and Z, seems reasonable. However, it's only X because I listened to it a lot a while ago.
So it's pretty good if you are listening to the same music genre, however, it sucks if you like to change the music based on your mood, etc. I also noticed that it doesn't detect the language the music is in so I often get songs with lyrics in languages that I have no clue about.