iTunes is surprisingly buggy and there are a ton of things not accounted for (can add to a playlist with the "..." icon but not right-clicking, can add to the queue by right-clicking but not dragging, etc.) The release was probably rushed and will need some time to be polished, but damn is it terrible by Apple standards.
Perhaps the most disorienting thing so far was understanding that when you add anything to a playlist, it automatically adds it to your library. But if you delete the song from the playlist it still stays in your library. So if you wanna get rid of stuff from playlists permanently you gotta shift-Del it. I only understand how this even works because I've been using iTunes for a decade. Very unintuitive, honestly.
Hopefully as they gather data they will add popularity counters to songs. The main thing I'm missing from Spotify.