Jumping the Shark

So I was talking to someone the other day, and we were discussing a certain book trilogy. Now, it's one of my FAVORITE series, and I adore the books, but I mentioned that I thought the final book 'jumped the shark' just a little bit. (If you don't know what that means, Google it)

She said 'how can a book like that jump the shark? It's a fantasy, the whole thing is a ridiculous concept. Rather than get into a discussion (or, more likely, an argument) I let it go. This person is not a writer...