Physically the book is top notch for a self-published work. It's a solidly bound hardback, black-and-white throughout and liberally endowed with cartoons by Howard Tayler of Schlock Mercenary
One reason the book can get away with the cost of being a hardcover is that one of the authors, Tracy Hickman, has solid form in the D&D community. He co-wrote the original Ravenloft with his wife Laura and teamed up with Margaret Weis to create Dragonlance, both of which were ground-breaking products. His son Curtis brings bags of experience as a professional magician to the project and the book presents an entertaining selection of puzzles and tricks that can be applied to roleplaying games.
An XDM is an "eXtreme Dungeon Master" and this book aims to show you how to be one. Immediately this gives away both the author's background in D&D and their target audience of D&D enthusiasts. If you're not into D&D don't let that put you off though, everything presented here is easily generalisable.
The advice provided covers a wide range of subjects. The authors are big on preparation before the game session, but also recommend flexibility when it comes to presenting material and options to the players. They offer tools such as different forms of narrative structure, presenting movement between narrative developments much like movement between physical locations. There are useful guidelines on how to provide the players with meaningful choices, while also using the unfolding drama in the world around them to realistically constrain their options. The Hero's Journey from Campbel's "Hero with a thousand faces" is presented as a way to think about and plan for the character's experiences and plot developments throughout an adventure or campaign. Various tricks and puzzles are also provided to challenge and amuse the players, while also usefully covering the tricky grey area between the ingenuity of the player versus that of the character.
All of the subjects that are covers are worthy ones and are presented in an informative and entertaining way. That's no mean feat. However I felt that while the ideas are good ones there was too little focus on how to actually apply a lot of these ideas in a game session. The ideas themselves are not enough, time and again I asked myself "Ok, but give me an example of an XDM using this idea in a game session". There are some examples, and they're generally very good ones drawn from the author's experience writing Ravenloft and Dragonlance, but about half of the material seemed to me to be discussed in too abstract a way. Some of the concepts from the world of stage magic in particular seemed a bit disconnected from the world of the roleplaying table.
The final few chapters are given over to the XDM game system. This is an extremely stripped down system that again betrays the author's deep D&D roots. They even present a Basic and Advanced version of the system. The Advanced version sporting twice as many stats for example (two instead of one!). It even has levels, although they have no actual mechanical effect other than to allow the player to claim "As a Level X character of this class, surely I can do Y".
At first glance the game system looks like a joke and a waste of space, but actually I'm a huge fan. Not that I realy want to run this system, although I would have no problem playing it, but the game serves as a case study of how to break roleplaying down to it's basic components and expose a lot of the concepts and relationships that make a roleplaying game work in actual play.
There's a concept that I first came across on The Forge called the Social Contract. The idea is that while rolplaying games appear on the surface to be just about the rules of the game system, in fact the rules governing the social relationships between the players and the GM are at least as important. Much of XDM is about these social relationships. An XDM has huge power over the structure and progress of the game, and that implies an equally huge responsibility to treat the players with respect and take their desires and preferences into account. By reducing the game system to a bare minimum, the authors move the focus very clearly on to the social relationship and the obligations of players and XDMs to one another. Ok in a more formal system the rules say how a player can use stat X versus the NPC's stat Y and roll for a result, so theoreticaly more such rules formalise what players can do and therefore give them more options and 'rights', but the reality is that if the DM get's to determine the value of the NPCs stat Y then the DM is still very much in the driving seat. My only concern is that the real value of the game system chapters will be lost on a lot of the people reading the book and will just be ignored as being superfluous filler or treated as purely there for entertainment.
I'd recommend this book to anyone who plays roleplaying games as being a useful and fun read. Making stuff like this genuinely enjoyable to read is an impressive achievement. It's a bit pricey I suppose and for some people there's not a huge amount that's really new. On the other hand the ideas here are important ones and it's always worth re-considering and reviewing how to approach roleplaying games and what we can do to hone our GMing (sorry DMing... Er, I mean XDMing) skills.