I haven't used it in a while, but this was a big advantage of Pandora for me. With pandora, you start a 'station' with a few seed songs and as you like/dislike songs, it keeps refining the station.

The downside to Pandora is that you can't choose your music. You can seed a station with a specific song, but that song might not be the first one played.

What I really liked with Pandora was that it was really good at producing endless playlists for me to listen to at work or car rides. I was a paid subscriber when I worked night shifts and drove a lot more. Spotify stations are really hit or miss. Sometimes the Spotify stations dive into foreign music and I can't find a way to specify which language of music I want to hear.