Piers Anthony Disease

A literature phenomenon in which the first book of a series does so well, and may even be considered a classic, that subsequent books in the series become staggeringly formulaic, to the point where the only difference between it and the last one are maybe location, names of characters, and point in time the story takes place in.

Named for Piers Anthony, author of the Xanth series, one of the most notable instances of this phenomenon.

"I really liked Frank Herbert's "Dune". It was honestly a well written story, its just that his other books got quite... similar afterwards. Same general plot, message, almost everything but the names."

"Ah, so he contracted Piers Anthony Disease?"

"I'm afraid so..."