From the Store description:
With Mus'box player you can easily access your music collection and play them. All music files are automatically sorted by 5 categories (artists, genres, composers, albums and songs), so you can always quickly find the desired songs. As an added feature you can navigate through your music folders and play them. Of course you can create your own playlist as well.
The simple and intuitive user interface can be easily personalized. It is possible to change accent color and background image.
Here's Musbox UWP in action:
You can grab this in the Store here. Getting rid of the ads forever is £4 in the UK Store, or you can pay half that (£2) to get rid of the ads for one year. Which is all fair enough, except that I do question whether there's enough here over and above Groove Music to warrant switching in the first place. Do you want custom backgrounds and easier playlist set-up that much?
I've also been playing with Neutron Player UWP, which has a truckload of pro-audio enhancements but also a load of UI bugs. Watch this space!