One of the nice things about not being in a book’s target audience is being able to stand back a bit more and see what the author is up to, what’s happening structurally within a book or series, to generally chew on it a bit more. The House of Hades reaches its main intended audience perfectly: Kid One tore through it in just a few days, never mind school or much of anything else. A whole bunch of people are growing up with Percy Jackson and his friends as formative reading experiences, and I think that’s great. They’re fun, and they work well on several different levels.
Still, as I said, they’re not aimed at me. (Books that I would say are aimed at me, or people like me, include Ready Player One by Ernest Kline or Mr. Penumbra’s 24-Hour Bookstore by Robin Sloan. Maybe also The Magicians and its sequels by Lev Grossman, but even there I felt a little like I had aged out of his picture of an ideal reader.) The pace of The House of Hades is nothing short of frenetic; this is not a mid-series book in which nothing happens. At the end of The Mark of Athena, Percy Jackson and Annabeth had fallen into Tartarus. They have a classic quest through the underworld to find and close the Doors of Death, to make sure that any monsters killed in the upcoming conflict with giants and monsters stay good and dead. At the same time, the rest of the crew has to make their way through the Mediterranean world to Epirus and close the Doors from the earthly side.
This brief description shows one of the balancing acts Riordan has to pull off. Percy Jackson is his most famous character, but this series is a quest with seven demigods. Each is on his or her own journey and has to receive enough time in the spotlight to a reader to become invested in that character’s individual metamorphosis and contribution to the overall narrative, but not so much time that the book becomes lopsided. Second, it’s been made clear that the quest is for all seven. None of them will die before the final confrontations, if then. The characters face obstacles, but the author is not going to put any of them in mortal peril in the penultimate book. Younger readers may overlook this fact, but it may encourage older ones to skim from time to time.