In my earlier review of Storm Front I rather candidly (I think) pointed out that Butcher's Dresden Files books are pretty formulaic. However, with this one, he gets a better handle on the formula. Fool Moon doesn't feel forced, it's not trying too hard, and it comes naturally. It also seems to up the ante quite a bit. The villains are scarier, their villainy is actually disturbing, and the series as a whole gets both more serious, more comic, darker, and more fun all at once.
There's a scene in particular, where a werewolf is arrested, the full moon hits, and he makes the Terminator's stop at a police station look like a picnic, that is quite moving. Characters that I had thought were going to be recurring are literally torn to shreds. This scene, probably more than any other, typifies for me the escalation of things in general that Fool Moon manages to pull off over Storm Front.
There's also some quite early hints of the "metastory" that Butcher has been dangling in front of us for some time now. What? His parents "natural" deaths may not have been natural after all? Dresden's past is examined a bit more thoroughly, as are his weaknesses and foibles; the things that make him an interesting narrative character to read about.
All in all, Fool Moon is a clear improvement in Butcher's technique, his craft, his plotting, and his artistry. My concern about the series isn't that he hasn't managed (mostly) to keep that up over eleven books and counting and mostly improve as time goes on; my concern is that he's only about halfway through his planned arc. Already I'm starting to feel like he's dragging his heels on resolving "metastory" plot threads, while instead giving us the monster of the week (or of the year, as the case may be) with just a few crumbs thrown in to whet our appetite for the bigger picture story going on in the background.
We'll see. My worries aside, Butcher hasn't let me down yet, and Fool Moon is the first really good Dresden Files book; the one that took a decent but ultimately not that memorable concept, and turned it into a powerhouse.