Poweramp

The app has many themes and options to change the screen orientation, startup screen or add items to the menu. It’s available in multiple languages and it automatically loads album art for songs. You can change the cross-fade length, adjust replay gain and use multiple presets. The app can play various audio formats and it supports lyrics.
 
Moreover, it has multiple widget styles and a configurable lock screen, as well as tag editor. Mono mixing and balance features are available, together with a very complex equalizer. You can create playlists inside the app and set songs as ringtones on your phone. The app can pause playback when headsets are disconnected and resume on Bluetooth.