Stylistically, gone is the comedy that was A Spell for Chameleon, and also gone is the classic adventure of The Source of Magic. With Castle Roogna comes the final pieces that makes Xanth the juvenile series of the late 20th century, those being a coming of age story, the forced and gratuitous use of puns suggested by the fans, and a new lead character every book. The lighting is now gone, replaced by merely competent writing.
Castle Roogna disappointed me in my youth. I wanted a book about Bink and only about Bink. A trilogy involves a character that you like across all three books. To switch character is book three just spoiled my day. I could not forgive that in the book. That, I just didn't care about Dor. On rereading the novel, I found myself still unable to care about Dor. The further that I read into the book, the less that I cared. I found myself reading this book less and less, not more and more. By the end, I was glad to wrap the book up.
I must complement Piers in his ability to both open and close a novel. Although the middle lost me, he did quite a job at interpolating the whole affair. Interpolating is a technique often used in the Bible where a scene is given meaning by including information on each side of it to give the scene context. Piers uses this technique as well, using it to give the story context. His conclusion is also particularly nice, as he has many threads to wrap up and he wraps them all up quite naturally and well, down to the apparent contradictions that the novel suggests. If you want to improve your wrap-ups, this is a good novel to study.
As an adult, I now understand all the sexual references that the author never explained, for Piers always left the most detailed sex scenes to the knowledge of the reader. In this, Piers shows himself was quite the classy writer. It is this very suggestiveness that allowed youth to read his books and cracked open the audience for him.
It is noteworthy that this is the first Xanth book written after A Spell For Chameleon had been published. In this book, Piers had already received fan mail from his readers and had already learned a great deal about what his readership liked. Intelligently, the man gave the audience what they wanted, and kept his mouth shut on topics which were too explicit.
Sexism rears its head in this book as well. The man was clearly writing for boys, not yet knowing how powerful of an audience that girls would turn out to be. I think as the years went by, he came to appreciate that girls did read his books and he strove to increasingly use them as primary characters. What's obvious here is that he did not yet understand how to use them, although that I can't say that is entirely true. When Dor appears as a barbarian in Xanth, he essentially writes a book that could be called A Barbarian in Xanth. It's a story that plays comedic homage to the barbarian trope, where his muscles destroy all comers and women throw themselves at the manly man. Here, Dor is never comfortable with his manly man-ness, and winds up succeeding by the use of his mind, not his brawn.
I will still accept Castle Roogna as an entertaining read, if not better than average, but I would not put it into the top tier of fantasy books. In my opinion, it misses the mark, alternately over-thinking and under-thinking too many parts of itself.