The worldbuilder has a lot on his or her plate. From deciding whether the planet should be Earth-like or something completely different, to creating continents with their own geology, climate, flora, and fauna, to peopling the world with new cultures of humans (or something else), to inventing religions, histories, systems of government...not to mention things like magic, psychic abilities, advanced technology, and other deviations from the mundane world. Rosenfelder addresses all of these areas in this volume, offering insightful and often surprising details and points of advice. He even manages to cover mapping and illustration.
The book seems to focus on steering the reader away from cliches and other mistakes, sparking creativity, and providing a range of options in places where the reader might get stuck. The amount of details provided is remarkable, but the level of detail is uneven--in a given subject, we might get a general overview, a fine level of attention to certain specifics, or sometimes both at once (determined, apparently, by the author's interests and level of expertise). This is probably unavoidable, given the ambitious scope of the book, which is both its strength and its weakness. Rosenfelder's last book, The Language Construction Kit, was devoted to the single subject of inventing languages, so it shouldn't be surprising that a book on inventing "everything else" should have some gaps. I wonder, for example, if he would have been better off doing one book on planets and another on cultures.
A word about the section on illustration and 3-D modeling: first of all, this section covers pages 298-347, so keep in mind (if this stuff doesn't interest you) that before you get to that section, there are 297 pages worth of content devoted to other subjects. The illustration section is aimed at people who want to draw pictures of their world, but have little or no artistic ability. I think this target audience will find it useful; others probably won't.
Overall, consider this a crash course on a ton of different subjects that one should know about in order to create a fictional world the right way. If that's what you are looking for, then I recommend this book. It has its flaws, but overall I consider it a good resource and a good value.
A personal note: I'm in the later stages of creating my own fantasy world. I did it the hard way--which involved spending several years researching nearly all of the subjects this book covers. If that appeals to you, then you can probably skip this purchase. As for me, I don't regret doing the legwork, but if I had had this book a long time ago, I could have focused my research more effectively, and saved myself a lot of time and effort!