I had huge issues with reliability. The windows desktop app was the worst in that regard - it'd just go silent or shut down on me without me doing anything, and I couldn't get it restarted. The android app would crash a lot too, freeze up, not work with Android Auto, etc. And their support was worthless (compared to the great support at Amazon when I shop for everything else). For a company the size of Amazon, it just doesn't strike me as a serious effort.
This may be more of a preference thing, but I also hated when going to artist pages only to have all their works - albums, singles, compilations, live, etc. - lumped into one list sorted out by popularity. And it wouldn't separate bands/artists with identical names. The catalogue sorting in Qobuz was also really lacking, last I checked, but at least they can be forgiven because it's a small company - and they told me it's something they're working on. Tidal, Spotify, and Apple all do it quite well. For a company the size of Amazon, what's their excuse?
And it's not even much cheaper, now that Apple changed the game and forced Tidal to cut its pricing. Both have lengthy free trials.