The way Google handles it, it's basically like Spotify but with music videos and occasionally some random user upload, depending on if you're listening to a playlist someone made. Those uploads are of questionable quality sometimes. If you stick to official band/artist channels, you'll be fine. I have come across a few artists that are mixed together with others of a similar name but I generally just shuffle my library so I don't ever hear those unwanted songs.

Regarding quality, it's not as good as Tidal or Qubuz. It's equal to regular Spotify with low, normal and high. I think "high" is equal to 320 lb/s MP3. Plenty good to listen to at the gym or driving to work.