Music.app is a huge improvement over iTunes but it just completely lacks refinement.
As with most Apple products, anything that makes use of the network is a frustrating mess. Remote pages take an unreasonable amount of time to load. If you click Search, it starts loading the "browse categories" page and you will have to search a second time if you typed your search terms before that finished loading.
AirPlay is fantastic once it starts working. Getting connected initially is a nightmare. Sometimes speakers don't show up for a while, or they rearrange order while I am making a selection. There is still far too much "blocking" in the UI where a popup box will disable the rest of the Music UI while, eg, AirPlay is connecting.
On the touchbar (lol) the controls are sometimes on the right side of the strip, other times on the left side of the strip. Thankfully the fix seems to be getting rid of the touchbar, which is better!
I think discoverability for new music on Apple Music is just ok, not amazing. But, if you find something that you actually like, adding it to your library stops playback. Infuriating!