It’s hard to pin down what would make the perfect game, but ticking the following boxes would certainly help:
Small scope - no being the lone heroes saving the world.
Personal - playing characters that actually have lives and aren’t just archetypes.
Consequences - real, tough consequences for actions. No saved-by-the-GM last minute dice fudging, no punches pulled - you make a decision, you pay the price for it.
Shared narrative - being able to have a strong influence in the direction and content of the game both as players and a GM.
Real problems - dealing with real world issues, not just ‘save X from space demons’
Simple - rules that enable maximum amounts of improvisation with just enough randomness to keep things interesting. Rules that focus on what you do and why - not how you do things.
Friends - playing with people you trust and enjoy telling stories with.
Actors - not just friends, but people that want to be their characters, that don’t see an entire session spent having an in-character conversation as wasted time or dull.
Sustainable - able to develop the world and characters indefinitely if desired.
Fiasco comes pretty close to ticking all of these boxes for me though stumbles on some. Mostly I don’t have friends that find it enjoyable and it’s naturally short, single-shot helpings don’t lend themselves to developing long-term stories.
Numenera comes pretty close too, but I’ve yet really to play a game with people that want to play the same kind of game that I do, one that ticks all those boxes. I’ve come close and I think Numenera with the right people and setup could go the distance, but it’s yet to happen yet.
Now, this isn’t to say I don’t want to play, or don’t enjoy, games that involve saving the world and other larger-than-life adventures. I’m all for defeating the evil god-kings of the black desert or unleashing the AI from its high-tech space-prison. I just want real life to get in the way too - personal conflict as well as external conflict. Do you go to war, knowing leaving your family behind will put them at risk? Can you deal with what is happening to the development of your son as you drag him along with you on your mercenary missions because you refuse to give your planet-bound husband custody? These larger than life situations are more meaningful when seen through the lens of real-world, personal issues when the consequences of success are just as complex and difficult as those of failure.
So I guess that’s what makes my perfect game - choices that mean something, consequences that matter, and people that are willing to face those with you to tell a story that doesn’t need to have a happy ending to be something you can all enjoy.