Gardens of Ynn isn't so much an adventure as a bizarrely semi-infinite dungeon. Locations and features that are rearranged and recombined every time, a small horde of monsters and some great treasure and tricks all come together to create a lot more playable content than it seems at first glance.
Everything is done with tables, which I thoroughly love. It goes like this: when the PCs enter the gardens, you roll for the starting location on a table of rooms. As they explore, rolling on the table generates new rooms on the fly. You don't know what will come up next, and every visit to the gardens is different. There are 35 rooms, plus another table of 35 details, which includes things like 'rumbling,' 'hypnotic,' 'smouldering,' or 'predatory'. This changes the lay of the land on every delve, and adds to the replayability of the gardens.
Last time you explored the well-maintained orchid houses, but this time it's the INVERTED orchid houses?!
After these two rolls, you roll for 'events,' which includes random encounters, weather, strange sounds, treasure, and brand-new paths that can take you much deeper into the gardens or provide quick ways backwards.
Downside: I fear it could be too much dice-rolling in the middle of a dungeon for each new area, and flipping back and forth, and thinking about how to describe what the characters see, since you don't actually know what it'll be until the PCs get there. I can picture this slowing down play unless you pre-roll a few or are quick on your feet. More to come on this when I run it for my players (probably in, like, 2028).
The monsters are all good and span the range from 'somewhat normal animals' like moss-rats, to wild stuff like the puddings (which are actually puddings and cakes!), and again there are some awesome tables to roll on for some of the monsters, giving them TONS of variety: you could EASILY keep your players on their toes with "what the hell is this monster?" for multiple adventures.
The best part of the book, which sent me scrambling to open up a blog entry and write this review as soon as I was done reading the pdf, is at the end in Section 5: Useful Tables!
Horticultural Styles, Unusual Flora, Ynnian Alterations (mutations that make you more like the residents of the gardens), treasure tables which include a whole table of special abilities for the magic weapon you just found, I search the body, I search the flowerbed, Stored Food, and tons more...
I feel like you could learn a lot about a campaign world by reading its Stored Food table. This one certainly gave me the flavour of the place. All these tables are great and 100% worth the price of the book all by themselves. Every one is jam-packed with just plain COOL ideas.