I'm giving this book four stars because I enjoyed pretty much every word in it. So why not five? Because for the most part I did not come away from the book with any great insights that would change the course of my writing. It was a very entertaining read, especially Orson Scott Cards' section, but there wasn't anything terribly earthshaking in terms of the creative process. The one exception I will make in this claim is Jennifer Brozek's section on NPCs.
In her essay, Jennifer describes how the NPC can be used to display the thought processes of the hero. In one example she uses an injured horse, and what decisions the hero makes in dealing with it, to show what kind of a person he is. Later she uses another example with the hero's reaction to an object he finds on the corpse of one of his enemies. In other words, the NPC doesn't have to be an observer, making comments about the hero, it doesn't even have to be a living person, or a person at all. They are there to serve as a catalyst, to make the hero think, grow, show us his true self.
The other bonus I got from this book was a whole bunch of new books to add to my "to read" list. That was worth the read right there.
I definitely recommend this book. It's short, entertaining, full of interesting observations (which may or not assist with your writing), and may provide you with new sources of reading enjoyment.