This is without a doubt the most pretentious thing I have to say about it, but I feel like YBB is shaping up to be the Tristan und Isolde of tabletop games. It doesn't just offer something new and arresting; it changes the conditions of possibility for what ttrpg creators see as within the bounds of their craft. I'm staggered reading the pdf - unlocking possibilities through events outside of the game itself, material interaction with the book having gameplay consequences, long (ten year?!) cycles in real time that bear out differences in the game world... and on and on. The online tabletop is a beautiful bonus, turning this all-too-online gaming ecosystem we've found ourselves in into a feature rather than a compromise, but the book alone is a masterpiece.