I think I preferred Here, There be Dragons, The Red Dragon, and the Indigo King to this one, but not by much. The story is a little more far-fetched than the others (well, maybe not the Indigo King) and a little more forced, I think.
However, if you don't compare it to the other books, than it is really very good. The earlier books in the series set a bar that this one just barely didn't reach. On the upside, this book requires less knowledge of literature to understand.