The latest Dresden Files book may be the best yet. The action starts pretty much right away and keeps going. A few new bits of Dresden's world are introduced, and several loose ends from previous novels return (mainly to get further loosened, although a few are resolved instead).
It's also got me more excited for the upcoming Dresden Files game, as this novel suggests a few things about the wider world. This isn't so much that this is explicitly mentioned, more that there is some stuff implied that sparked game-style ideas.