I want categories like this, but I already have categories for each franchise. Anything that's related to a franchise goes into a category named for that franchise. Even if it's just a game and its soundtrack. That way, everything for a particular game is kept contained and I know what's related to what. If I have a random "dev tools" installer in my library, I figure out what game it's for (thanks to SteamDB.info and it goes into a category along with that game.

I do have a separate category for simulation games, but only because I love simulators and have tons of them. Outside of that, any attempt to make genre categories has just further confused my library. So for not, I just have hundreds of categories for specific games and their included content and/or sequels.