I guess one reasonable metric is how long I probably played it. Close Combat II: A Bridge Too Far and an old computer pinball game, Loony Labyrinth probably rank pretty highly.

Another might be how long after its development it's still considered reasonably playable. I'd guess that maybe something like Tetris or Pac-Man might rate well there.

Another might be how influential the game is. I think that "genre-defining" games like Wolfenstein 3D would probably win there.

Another might be how impressed I was with a game at the time of release. Games that made major technical or gameplay leaps would rank well there. Maybe Wolfenstein 3D or Myst.

Another might be what the games I play today are -- at least once having played them sufficiently to become familiar with them -- since presumably I could play pretty much any game out there, and so my choice, if made rationally, should identify the best options for me that I'm aware of. That won't work for every sort of genre, as it requires replayability -- an adventure game where experiencing the story one time through is kind of the point would fall down here -- but I think that it's a decent test of the library of games out there. Recently I've played Steel Division II singleplayer, Carrier Command 2 singleplayer, Cataclysm: Dark Days Ahead, and Shattered Pixel Dungeon. RimWorld and Oxygen Not Included tend to be in the recurring cycle.

[–] Flamekebab@piefed.social 1 points 13 hours ago

The greatest single-playthrough game would be a fun category. I think my picks for that might be What Remains of Edith Finch, Gone Home, Broken Sword: Shadow of the Templars, or Grim Fandango. Fire Watch would probably get an honourable mention.

A "pinacle of a (mostly) defunct genre" category might be a good one too. I would argue that Command & Conquer: Red Alert 2 is the best isometric RTS games ever made.