I haven't used Xbox music since Windows 8 RP. I was very disappointed with the lack of features in it back then, and looking at what the current version is like, my opinion on it hasn't changed. It's seriously lacking in options, and still looks very much incomplete to me.
I'm surprised there's no way to change the sorting of music when viewing by artists in your own collection. It just defaults to songs which is lame. It's also sluggish when it has a few thousand songs compared to Zune which handles it gracefully.
These two points have especially got me not very happy. If the comment about the performance being sluggish is true, then it probably wouldn't handle too well on my end, considering I have something like 3600 songs. That, and the fact that selecting an artist just lists the songs,and not the albums is a big letdown, as I've grown a custom to Zune's three column layout: artists, albums, songs. Heck, the music+videos app on Windows Phone 7 lets you view artist albums, not just songs.
Xbox music just feels like something that's only designed to be used as a basic music player, and only on tablets. As long as Zune works, I'm probably going to stick with it.