Still probably the best supplement produced for Mythras. If you want a detailed example of a Mythras campaign setting, Monster Island gives you a dramatic start. Every chapter starts with an extended quote from Clark Ashton Smith and so much of the material conjures up the atmosphere of Smith's Zothique fiction even though the jungle setting is not typical of his dying Earth world. The decadent sorcerer schools of the high folk exude the archaic vocabulary of Smith and the corruption of his sorcerers. The campaign is very much a sandbox which positions three major cultural groups teetering on the brink of conflict with each other (the colonists, the tribes and the high folk), with the players being thrown into the mix. There are a number of suggested starts for the players from a typical Conan-style sword and sorcery adventurers, to a 1930s film crew, to, in the author's own campaign example, the eighteenth century ship's crew of Captain James Cook's final voyage.
And there's a lot of monsters - about 1/3 of a book is a bestiary of creatures, most of which could be used in any setting.
Where to start, 5 stars, it is a huge 298 page sandboxy adventure for Mythras, usable all the way from Ancient Greece, Medieval, up to 1920's (Call of Cthulhu), or modern times (Delta Green), and beyond, I plan on using it in a "sword and blaster" type sci-fi setting with M-Space. Filled with dinosaurs, macuahuitl wielding serpent folk, and even Kaiju if you want them; a huge bestiary ranging from normal to supernatural monsters. Different terrain types from jungle to glacial peaks; ancient ruins, lost temples, tombs, settlements, and a colony town built in an ancient ruined city, that can be used to fit the character's background. New combat traits, and new magic. Cultures are fleshed out, lots of maps, and multiple encounters. Everything you need. Cheers!