There is one thing that MS don't seem to do well, it's revision and keeping progress.
e.g. Music player - Zune Music / Xbox Music / Groove
WP 7.5 - WP8; Music was overhauled and EVERYTHING good about Music/Xbox Music at 7.5 was lost. Album Art sync, all tagged and favourites, lost.
WP8.1 - W10m; By 8.1, they've got it back to how it was-ish at 7.5 for music, but guess what? They've screwed it up again, on top of loosing BT AVRCP 1.4 - which was a godsend when I use my phone as main entertainment in my car, Groove takes years to launch via tapping / Cortana.
I am still happy with my 640XL, but when W10m and its basic music function don't improve this time next year, I will most-likely leave for something less annoying everytime they 'improve' in revision!