After book two in this series, the story moved from UF/Crime/Investigation with fantasy to Fantasy with elements of Investigation. My declining ratings reflect this change. I enjoyed the early connection to the police and the elements of criminal investigation in the first couple of stories. Starting with book 3 and continuing to book 5, it's Harry Dresden vs. the world/underworld/supernatural world/fill-in-the-blank world.
That said, I have accepted the story changes and I enjoyed this book for what it was. Death Masks takes a darker turn that some of its predecessors and reintroduces us to his, now, butt kicking half vampire former girlfriend. Nice touch Mr. Butcher.
There is less magic in Death Masks and Harry spends more time running for his life. In that sense the book was interesting as Harry is aware that there are things he cannot fight with fire or wind.
I can see why so many people give this series a 5 star rating. If I was a fantasy freak, I probably would as well. I am still enjoying and will continue onward.