I tried it very briefly, when it still brand new, because the regular client didn't support replaygain. Found the UI/UX quite complicated, because of the super minified controls. Has anything changed in terms of that?
Plexamp was launched twice, first as a Plex Labs desktop-only app, then completely overhauled as a cross-platform app with 'droid and iOS releases.
It has changed a lot since, the UX is much smoother now, with tons of new settings + features implemented. There's no other selfhosted solution that comes close IMO
UI is still a bit complicated. Plex uses its own implementation called loudness leveling rather than replaygain. I've found it to be just as good for the most part.