I am a big fan of Google Play Music, I love the instant mixes and find the whole experience much better than the Xbox Music app (hopefully improved in Windows 8.1). The web version of the app works ok on Windows RT/Windows 8 but a better experiences is via gMusic for Windows. The Windows Store app has been updated with improved search features and better integration with the All Access Radio features.
The app is free from the Windows Store.
06/17/2013 – Version 2.2
[+] All Access Radio Support (Create / Delete / Rename / Listen).
[+] Improvement in sorting and searching for names with “The” in names / titles (e.g. “The Prodigy” is equal to “Prodigy”).
[b] App can crush after adding songs in existing queue.