One of the questions I have continually thought about is what I want a roleplaying game to be like. What are the optimal features that I imagine in the "Hypothetical Favorite RPG"?
Non-binary success
After the players roll the dice is isn't just one of them succeeds and the other fails.
Examples
Wagers from Houses of the Blooded
Arbitrary Character Elements
Your character should have things about them that give them mechanical bonuses which are character based and can be almost anything that the player wants.
Examples
Aspects from Spirit of the Century
Fortes from Swashbucklers of the 7 Skies
Dogs in the Vineyard
Rewards for attempting difficult tasks
Very difficult rolls should have some benefit to the player. Higher difficulties should have some reason the player does not want to avoid them and try for easier rolls.
Examples
Advancement in Burning Wheel
Player involvement in narration
The players should have some ability to narrate and add things to the story. These are things that are beyond just their character's ability to interact.
Examples
Wagers from Houses of the Blooded
Goal driven characters
It shouldn't just be the GM telling players where to go. The players should also have input on the flow of the plot and what they want to happen.
Examples
Beliefs from Burning Wheel
Characters of differing skill levels
There are many stories where the hero is trained by his more skilled colleges. I want there to be both weak and strong characters in a group and not have the players feel like it was unfair.
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I'll add other things I want in a game as well as more examples as I think of them.