I've been on Google Play Music (and now YT Music) for ~8 years. YT Music has a different catalog (by my estimation it's less complete than GPM's was) and also lets you pull up songs/videos from youtube (which can't be downloaded for offline listening like other songs, and are just kind of mixed in with everything else).
Artist and album descriptions are largely gone, and so is the ability to view your listen count of songs, or sort songs in your catalog by listen count (which was my favourite feature of GPM). I suspect they're doing this because they've changed their accounting to get away with paying artists less (the % completion rate to 'count' has changed, or perhaps they're not counting some listens altogether)
The one saving grace of YTM is that its predictive playlists are actually pretty decent, and there are a lot of them.
