Honestly I think this app is quite good for managing and listening to locally stored music libraries. I've never had a issue with it scanning and adding all my music to the app. I just go into settings, tell it where my music collection is, and it adds it all. It's all organized and labeled correctly. Has album art for everything (including collections I put together my self and added my own album art to). It even auto downloads the covers to some albums that itunes can't find the cover for.
Functionality wise it works perfectly fine. It's fast, easy to navigate, looks nice etc. I really don't see what there is to hate. It seems to support plenty of file formats. Most of my stuff is MP3 like a lot of people but for the bands I REALLY like I have FLAC files and it handles those just the same as well.