I have a large mp3 library and have used Marvis for over a year. Marvis is great and extremely customizable, but it has a few bugs and the developer has abandoned the app. I won't use any music app that doesn't allow shuffling by album. It sucks that Apple bastardized the main music app to promote Apple music; I think that app was at it's best around iOS 7.
You should check out Cesium. I've been using it for the past couple of years. It accesses your music library, so all your music and playlists are there. You can play by album (and shuffle the music) or even play by artist (and shuffle all songs by the artist). You can even play by genre if you so desire. Of course it provides all the typical music queue management facilities as well, but I don't tend to use those too much. I like it's extreme simplicity.
The Apple Music parts can be disabled in Settings. It's not quite as nice as it was back in the day, but I've found that doing that helps to make it closer to how it was.
