This is not going to be a great review, because I read the book at my maximum speed, which is fearfully fast. And it's late, and I just drove to Frostburg and back (6 hours plus round trip).
Much of what I liked in the earlier books is there: the distinctly drawn characters, the slightly mad humor, the wonderful names, the page-turning story. As with the previous book, this one takes a while to really get underway; lots that is intersting and amusing happens in the early chapters, but you don't get much of a sense of forward plot motion. When the plot really kicks into gear, though, it takes off like a runaway freight train.
This is no longer totally a kid's book; it has definitely stepped into YA territory. There is a lot of moral ambiguity, and Harry is forced into a lot of uncomfortable realizations. Harry goes through a lot of teenage agnst, and depending upon your perspective you will either find this very tiring or all too realistic.
In the end I liked it a lot, but I'm going to need more time to sort it out. The plot is quite complicated, and there's also a lot of data dump scattered through it (one reason why it's so long).