In Fool Moon the reader can sense that Butcher is settling in to this new (to him) style of writing and becoming familiar with his protagonist and the world. There is a sense that he's spent hours figuring out the world and the characters, and there's always a bit more beneath the surface than we get to see, which keeps the intrigue moving from book to book instead of just throughout a single novel.
Butcher approaches werewolves in a slightly different way than I've seen before; each different word for a werewolf--hexenwulf, loup garou, etc.--denotes a different type of wolf, and he deals with four different types in this book. Dresden also wrestles with his responsibilities as a teacher, a mentor, a friend, and a consultant; how much is safe to tell any of the people in those relationships? What will happen if he doesn't tell them everything? Actions have clear and often devastating consequences, and Butcher does not shy away from them. This is not a happy book, but it is a good one.