Hello, I've been using Spotify for 2 years now and it's improving, but still junk compared to similar apps.
Here's a tip to make it somewhat less frustrating:
Somehow, the developers geniusly decided that a user shouldn't be able to see his library (desktop version) and playlist on a full page, like in the mobile app. They just assumed that people won't have more that 15 entries in their library. Well, they're wrong: I have 50. Try searching the entry you're looking for in that mini field on the left and not get frustrated... if you think that's fine, you're a masochist as a user and a sadist as a developer. Please, for the love of userability, get your heads out of the ground and solve this.
Solution: make the Library and Playlist titles on the left clickable, which leads users to a full screen with these. So what you have now would work as a small view of the real thing, which could be located in the browse section. And you get there by clicking on "Your Library" or "Playlists".
ps: bonus tip: try playing around with Soundcloud (mobile), which is an actual intuitive app.
Especially their simply fantastic and definitive way to navigate in a song (with one hand!!): you can see the sound waves, which makes it easier to get to the point you want to hear.