This is an outstanding supplement to a very well-deseigned tabletop RPG. It is about the same length as the core rules, so with this book one basically doubles the amount of source material available for playing Ironsworn. It adds an entire, completely option, but incredibly cool set of moves and quests to Ironsworn that allows the player to add greater variety and detail to the gameplay. It introduces new "denizen" species of the Ironlands, and it even provides a large number of "pre packaged" Delve sites and maps out their locations, in case the player would rather use a more developed world than generate one de novo. I personally prefer to generate my own, but I have to say that the ones Shawn (the author) provides are quite interesting and add a ton to the atmosphere and setting of Ironsworn.
Once again I am blown away by the quality of not just the rules but the setting. As someone who normally hates it when RPG writers mix their setting with the rules, no one is more surprised than I am that I would say such a thing. But the setting is so well thought out, and dovetails so perfectly with the basic gameplay of swearing iron vows and all the rest of it, that I am incredibly pleased that Shawn put them together as one, and did not separate them into 'gameplay' and 'setting' books.
You can, of course, entirely ignore the setting and do your own homebrew world without any problem at all. You don't have to do "Iron" vows or live in "Iron" lands (people on the Discord have names like "bloodsworn" for blood vows, and maybe living in the bloody lands or something similar, for example), but I certainly won't be ignoring the setting in my game play. I love it to death and can't wait to see even more.
I love this book and its predecssor (the free-to-download core rules) so much that even though I already own the full PDF versions, I just today ordered hardcovers of both. I did this partly because I like physical books, but partly to show support for the author -- here's hoping he keeps making Ironsworn-related supplements for years to come.