iTunes is now featuring an edge-to-edge design. Clicking on albums results in an expansion like folders on iOS. Inside that album is a feature called 'in the store' which shows top songs and albums.
Artists can now share photos through iTunes. Currently playing now shows what's coming next, a cool feature, albeit a bit unneeded.
iTunes also has a new mini player design. This could be really nice as it allows you to manage playlists and upcoming songs.
iTunes gets built-in iCloud and new, streamlined store like mobile iOS has received.
Becomes available in October.