I like Google Play Music, a lot, but:

    - Google. Privacy.
    - trying to shove the Android/Material UI on iOS, such
      an impedance mismatch... I *hate* that.
    - no dedicated client on desktop (so, no offline mode)
    - the UI in the browser sucks (again, alien, and basically
      *negative* information density if it could be so)
    - uploading/downloading is a crapshoot[0] with official tools,
      and the API is unofficial so hacks[1] may be short-lived.

So, again, I like GPM (and GPMAA) a lot, but only on Android.

The only thing I miss in Spotify from GPMAA/Apple Music+iTunes Match is the digital locker for seamless syncing of music I own.

FTR, despite having a native UI and digital locker, I moved from Apple Music to Spotify because discovery and reliability were terrible.

[0]: official tools behave similarly to this: https://github.com/simon-weber/gmusicapi/issues/140

[1]: https://github.com/lloeki/ruby-skyjam