K. Im going to focus on TTRPGs for the momment because thats what I can wrap my head around.
Dice Used (Standard set, multiple Standard Sets, 4dF, 2d12, *d6 ).
Main Die Mechanic (Roll Over, Roll Under, Dice Pool, etc) [ Man the ability to sort games by the dice they use kinda excites. ]
License ( OGL, Creative Commons*, Standard Copyright, etc, etc).
Sexually Exploitive Art
Sexist Mechanics (strength caps on female characters, etc.)
Legal SRD Available
Rules Crunchiness (This is very subjective, not sure how you’d quantify this. But its a big factor for lots of people and me. ?)
Publishing Strategy: Everything in one book / versus multiple core rulebooks and lots of supplements.
Battle Matt (Optional versus Heavily Encouraged versus Nearly Mandatory)
Officially Supported Campaign Settings
Community Supported Campaign Settings
Explicitly Progressive ( Games highlighting diverse characters and explicitly defining their worlds with broad definitions of equality. Pathfinder and Blue Rose come to mind here, there are of course others. ).
Classy versus Classless characters.
Levels versus Leveless characters.
Influenced/Inspired By (How 13th age was very much a different take of the 4e design philosophy. How Fudge was inspired by GURPs, etc.)
I’d like something to capture narrativist versus simultaionist. I.E. Story-driven-mechanics versus simplistic physics sandboxes. However the deffinitions of narrativist versus simulationist have gotten so muddied i’d like different terms for this.
I’d also like something to capture games with known toxic creators. Like Lamentations of the Flame Princess gets tossed around the internet, but id like to slap some surgeon generals style warnings about both the creator and publisher being scum.