Some disorganized thoughts to mine for ideas:

• It's definitely possible to classify most TTRPGs within existing storytelling genres. Is there any kind of standard list of genres that appeals?
• A lot of TTRPGs are based on specific systems - e.g. Wretched & Alone SRD, Carta SRD, Peregrine SRD, Princess with a Cursed SRD - and tagging this systemic origins can be helpful for finding specific kinds of games.
• When we were trying to do this, we also tried to tag games by number of players. We never finished structuring things or making a form for adding and editing games, though.
• URLs change, but it still might be good to include them.
• Special equipment - conspiracy boards, tumbling block towers, Tarot cards, etc. - were another thing we were tagging.