Generally very happy with the app and don't have any problems with it. My biggest pet peeve however is how easy it is to UNLIKE a song. I'll either be listening to a song and notice that it somehow become un-liked or I'll accidently move my finger and un-like it. It's not a matter of life and death, but I don't like how this mixes up my Liked Songs playlist, as re-liking songs takes them away from the original group of songs I had like at the same time (like from an artist, album, or mood creating a new playlist).
What makes it a bigger pet peeve is that Spotify is now a big and very popular company, so I'm surprised this hasn't been brought up or addressed yet. I can't imagine they want people unliking songs without meaning to, and I personally think even just making it more difficult to unlike a song would be beneficial. Like holding down the like button for 3seconds, instead of a single tap.
That's my review. Spotify is great, I use it almost every day, just hate having to relike songs I didn't mean to or didn't know I unliked.