If you want to see the problems then try these links:
Master list of issues:
http://answers.microsoft.com/static...c-on-wp8/b1c64834-de43-4af6-8069-4626090289a3
Master List of Issues (the return)
http://answers.microsoft.com/static...perience/2cc28d2f-d5aa-4840-8cf8-8129f5577546
Zune Uservoice Suggestion
https://windowsphone.uservoice.com/...058-continue-to-use-zune-for-media-sync-in-wp
My WPC Thread (Xbox Music - Enough is enough)
http://forums.windowscentral.com/groove-music/217754-xbox-music-enough-enough.html
The Major Issues relate to syncing and music management
1) Duplicates - there seem to be many causes for this problem, but MS never addresses it.
2) DRM issues - WP8 regularly incorrectly tells you that you don't have the rights to play music (many times the first track of an album).
3) Metadata issues - if it doesn't recognise a track, it won't cloud sync it. You have minimal control of the metadata etc and XBM will have no problems with overwriting your music collection's metadata with its own, and introducing DRM in the process.
4) The syncing situation is totally disjointed. There is no one problem free method of managing your music (many people find the best way is with iTunes!?!?!).
5) The dedicated sync app is a total joke.
6) Managing playlists is a near impossible task.
7) No podcast support
8) The cloud sucks! There's no easy way to manage what's in your cloud music collection.
9) It's bad for pre-owned music. If you owned the music before using XBM, then if you sync from the cloud, then you can only stream it to your WP - there is no download option (this is bad for your dataplan, your battery life, for listening while travelling or if your happen to be in bad reception areas).
10) It gets easily confused with what's downloaded and what is streaming. I've seen it say that the track is downloaded, but in fact it streams it anyway!
11) Lack of wireless sync. Zune had wireless sync, which was completely seemless.
This list is by no means definitive either.