Island of Fire Mountain is given the code DW2, it's the second Dungeon World adventure by Johnstone Metzger though it doesn't directly connect to or follow the events of "DW1 - Lair of the Unknown" and after the scenario presented in that first adventure you could be forgiven for assuming that this module is a callback to another famous D&D module. It definitely has some similarities but the inhabitants and plotline are wholly original.
There is no railroading and there is no predetermined mission for the island. If this adventure had been published as a Labyrinth Lord (or any other similar OSR rule system) module then it would probably be classified as a hexcrawl. The booklet consists of five parts; an introduction laying out the island with ways of landing the PCs onto it along with two fronts for creating conflicts with the colonial inhabitants and the tribal natives, a section on the colonial fort that has been practically abandoned but is still occupied by desperate ne'er-do-wells hoping to find a way off the island, the middle part describes the island proper with all of its natives both humane and monstrous, the fourth part describes a ruined city at the base of the island's central volcano in the heart of the jungle, and the last section is a collection of custom rules and a new class to introduce to your game if you feel they're appropriate.
This book is brimming with possibilities. There is no central plotline or story, but there are conflicts that could arise and there is plenty of legroom for a creative GM to take what is here and mold it to fit around her PCs. I kept finding parts of the adventure really inspiring and I repeatedly found myself wishing I was running a game this weekend. Many of the monsters are unique and provide plenty of healthy challenges even before the stories of the NPCs might warp or twist the goals of the players. I love-love-LOVE the Cyclopeans and their strange connection to the cannibals on the island, I would probably use them outside of the adventure if I could get away with transplanting them to multiple environments.
The elementalist class at the back of the book is very cool and interesting, but many aspects of it are vaguely written and I think it's the weakest feature of the book. There are eight tables of grim portents scattered throughout the module and I can't tell you how many times I flipped through the book reading the portents, looking at the NPCs, and studying the map. I was really taken with this adventure, perhaps because I like the idea of stranding some hapless adventurers on a wild and savage island with little to no hope of escape.
You can purchase pdf and print versions of "DW2 - Island of Fire Mountain" at DriveThruRPG or just a print version at Lulu
Johnstone Metzger also has a blog and a patreon campaign for writing up monsters in Dungeon World and Labyrinth Lord stats