This book is pretty killer, especially the illustrations. I read the first two books already, and helped playtest an earlier version of this product.
As far as their previous work goes, this one is the best yet. It explains how the rules work in fairly clear detail, and is organized from front cover to back cover in a sort of adventure sequence -town, journey, dungeon, combat, experience. It did come out weeks later than promised. But, I have to say it lived up to my expectations and perhaps exceeded them. And well, at $10 it beats most other products out there straight away for solid value.
I really like the amount of detail that went into the overland terrains and the different types of dungeon. They're clear cut, and define the setting fairly well. Plus they come with tables for random generation. This is something other systems need to do.
There were a couple of references to products that have not yet been released. I'd love to see the terrain hazards, random encounter tables and on-the-fly dungeon generation tools that are supposed to be in an upcoming Master Codex. Plus, it would be really good if they had some more monsters to throw at players.
Most things are a little better worded than their previous products too, plus they've updated everything to something called COG system. It seems the same overall, but has amalgamated a lot of the redundant rolling into faster game mechanics -you don't roll for damage anymore cause it's already part of your attack. Oh, and an important good change was the skill retries which I found in their updated Character Codex -you can retry as much as you like, just by paying 10 Steam each time. Much better. There is no need to calculate encumbrance or armor penalties in this system (my group always ignored them in any system anyway) -bravo! All in all, the system seems better, easier and probably faster, though I can't say for sure until I test it.
If you're worried about trying a new system, it's quite logical -we worked it out pretty fast. You need the three core books, and use the index and the bookmarks.
Apart from a minor gripe that the massive illustrations kill my printer cartridges, I'd recommend this book to anyone. Ten bucks (thirty bucks for the set) is cheap for an awesome setting and probably about a hundred full-page type illustrations (no kidding). Even if you don't play it -the setting can be ported into any other campaign and is really cool. Good job Flightless Terror!