Most of my music listening is on portable players (AK100/DX100/50 are favorites). But I've purchased a new computer and returned to Windows as I wanted a tablet convertible. Settled on a Asus Taichi 21. After installing all my required apps, I turned to my music files and was disappointed to find the default music player, XBox Music doesn't recognise my album art. In fact, not many MS Store apps I tried do. They all seemed to want connect to an on-line service like Last FM and that failed to register more than maybe half my albums cover art. Searches for "Best Music Player App for Windows 8.1 Metro" was disappointing to say the least. Nothing much came up and even hear at Head-Fi I couldn't find much to recommend.
So after much scrolling through and trying a couple of recommended app, none of which displayed much cover art, I found Mediamonkey have written a Metro app and posted free on the MS Store. Its pretty darn good and comes with a host of features including all the usual things like Playlists and so on. Nice that it loaded all my cover art (it must be embedded by the look), has a nice interface and most importantly, easy to navigate. Also nice is the ability to explore local and removable drives and play albums from there. Lots of configuration options and you can customise the colours of the interface too.
Not a full review because I need more time for that but thought I'd put up a post for others like me looking for a Windows 8.1 media player. So far I'd give it a 4/5 stars and may earn more later.