First, a good friend of mine wrote this, and I liked it so much, and think it summarises what the setting is all about so much, that I'll share it:
Perhaps something else no-one has said is how much Yoon-Suin is about beauty.... All of the sights in it are picturesque. Very like an orientalist painting. Even the very horrible locations are a little more ripe than harsh. And the culture depicted in Yoon-Suin is about luxury and about beauty. Its relaxed instead of tight, slow instead of quick, warm rather than cold, lit rather than dark, sad rather than grim, opium not cocaine. Some RPG settings are created, in the manner of Apocalypse world, on a kind of energetic tilt so that whatever the PC's do when they wander into it will have deep ramifications, the world will spin around them. One gets the sense that, no matter how the DM constructs it, the world of Yoon-Suin is not going to change very much regardless of what the players do. The opium barges will still drift down the Yellow River, the slaves will still have rubbish lives, the Slug Men are not going to be deposed from the Yellow City. (Who would bother to? And who would replace the Slug Men? Calm down and have some tea.) The politics of the Hundred Kingdoms will always be chaotic and the chaos will never change. The PC's are simply moving through this world like everyone else.
Second, a number of people have said they have bought both the PDF and print versions, or are thinking about doing so. I'd like to give those people something extra, so my plan is to send them a free PDF Yoon-Suin dungeon that I created for a game. This is The Halls of the Shimmering Stars in the Deep Blue Firmament, and is a three-floored palace with approximately 120 rooms total. If you have bought the PDF and print versions of Yoon-Suin, then email me (jean.delumeau AT gmail. youknowtherest) with your order numbers from payhip/drivethruRPG and lulu, and I'll send you the dungeon when I've typed it up and scanned the maps.