Nokia stated that the Windows 8 version of Nokia Music+ features:
A 7 day trial of NM+: With an in-app upgrade path (30 second clip mixes outside of the trial period)
100's of curated mixes from Nokia experts and international artists
Listen to all the MP3's in your "My Music" library via the app
Mix recommendations based on the music playing, for both mixes and your own collection
Artist mix: See up to three artists, and the app will create a playlist based on your choices
Offline mix: Save as many mixes as you can carry for offline playback
Search for mixes containing your favorite artist
Artist pages: Complete with high quality artist images, biographies, tweets, gig info (including Here mapping), related artists, and more
Snap View: Minimise Nokia Music on your home screen, but still access music controls
Play To: Stream music to DLNA devices on your wireless network.
As you can see, the only way to enjoy Nokia Music on Windows is to be a Music+ subscriber. The fee is only $3/month, which is much less than any other music subscription service. It's interesting that Nokia is making this available for non-Nokia devices since you still need a Nokia Lumia smartphone to use the service on a phone.
Nokia Music for Windows 8 is available now from the Windows 8 Store in the UK, US, Ireland, and Australia, and will be rolling out to all counties with Nokia Music+ in the coming weeks. If you are already a Music+ subscriber, then you can just sign in with your same credentials to enjoy the service on your Windows 8 or RT device.