Great Novels That Don't Work

Which marvelous masterpieces of science fiction, fantasy, or horror don’t really measure up? Why? Do they feature faults that genre fans forgive more readily than regular readers? Did these stories get sprinkled with plot hole dust by the That Don't Work Fairy? Are they still great, in spite of not working? Or even—as in the Japanese philosophy of wabi-sabi, where flaws perfect the whole—because they don’t work?