You can listen to it here: https://c418.bandcamp.com/album/minecraft-volume-beta
I listened to it all today and it's all quite excellent. It's very much in the same style as the peaceful piano music currently in the game but with a bit more variation. I feel like it's actually a fairly big improvement, C418 has gotten much better as a musician over the years. Track 16, Taswell, is a tribute to Ryan Davis and is one of my favorites of the album. None of it is implemented into the actual game yet but hopefully it happens soon.