It amazes me that the 9th book in a series could still be going so strong. There were a couple of plot stretches in this book that I wasn't entirely OK with, but overall, it was excellent. The series is definitely getting darker, but not too dark.
My only complaint, really, is how easily the whole Lasciel story arc was completed. This has been a multi-book arc, and ended entirely too neatly. If it were an in-book plot thing, I could live with it, but no, it was too neat... too tidy.
Otherwise, another excellent installment of the Dresden story.