I'm going to say Wanderhome. I ran it because a friend wanted to try it on her stream, and I'd heard good things. But reading it, I was surprised by the fact that the game has almost no rules. Like I'd played "rules light" games, but this was a whole different level. Instead, it tries to hang the game on tone, setting, theme, prompts, and mutual trust between players. And like what the book did, it seemed to do well, but I was very worried about whether that would all result in an actual game. But to my surprise, it went perfectly smoothly. It's really made me question what makes something a "game" and what a game actually needs to work.