I would be interested to learn what kind of playback solution you use.
I also find genre designations mostly useless: About 60% of what I listen to falls under the country/roots/americana/bluegrass/folk/folk rock -umbrella. I see no intellectual value in attempting any more granular systematization - especially since that would force me to label stuff on a track-basis instead of an album or even artist basis, which is incredibly time-consuming and fucks with playback software.
However, simply pressing shuffle/randomized play on my entire library and doing away with categorization alltogether isnt satisfactory either: I dont really want to listen to Five Finger Death Punch while relaxing before going to bed, or to The Little Drummer Boy in the middle of summer.
The solution would obviously be to make use of the "mood"- instead of the "genre"-tag: mellow / upbeat / pathetic / sexytime (#humblebrag ?) / etc. I havent found any playback software on mobile (Android, unfortunately) and desktop (Win) to access that mood tag though...
On windows, I use foobar2000 for playback (bulk tagging on windows is done with the indispensable mp3tag software). I have been meaning to give roon another try but have not got around to doing so yet.
I almost exclusively listen to full albums and generally browse by album artist so my library setup is quite minimal- a listening session for me involves manually scrolling through my collection and picking what album I am in the mood to listen to. If I don't feel like listening to anything in particular I queue up new albums that I may not listened to yet or search for new music, which usually involves further researching an artist in my collection I don't now much about, finding other artists associated with them, or finding similar artists on youtube/streaming services.
Foobar is highly customizable (maybe
too customizable) and you can choose to list, display, or search by non-standard/custom embedded tags no problem. On android I use USB Audio Player Pro which is probably the best music software for android but I believe the library cannot be viewed by custom tags and only be viewed by the standard album, album artist, genre etc. (it also has a playlist view). One solution to your problem would be to just reappropriate the standard "genre" tag as your de facto "mood" tag, so that there is high compatibility with most common software if you access your collection with multiple apps/devices.
I don't personally use them but I'd think the most obvious solution would just be to go through your whole collection and just make playlists for your various "moods" in your playback software of choice- that's essentially what playlists are for after all. You can then shuffle your playlist, play it by album, sequential order etc. with ease. Practically all playback software has a playlist feature.
Coincidentally, I am listening to a Christmas album in summer. I must be depressed.