I finished The Battle of the Labyrinth. Now, you know me: I've gushed about Rick Riordan's series before. This time, it's less of a gush and more of a stream. Why?
In part it's because of the nature of series books - they become formulaic. This is very true in the case of the Lower School series we buy (like The Secrets of Droon or Magic Tree House), with a relatively controlled vocabulary and action. That's great for very young readers, because you want them to become comfortable reading and this is a great way for them to do that. As an older reader, however, you don't need that sort of scaffolding and you enjoy a challenge.
Now, I have to admit, there is a sense of comfort in the cozy mystery genre. Reading a Miss Marple means that you have general sense of the structure of the upcoming mystery; ditto a "Death on Demand" or "Puzzle Lady". Even a series like Ian Rankin's Rebus books have an expected arc (and you can say the same about books like Marion Zimmer Bradley's Darkover series, or Kathryn Kurtz' Deryni novels). Reading a book like this is like eating comfort food, isn't it? Many of my students will come in asking for "a book just like ___", by which they mean a book that has the same arc, the same essence as the book they finished.
There's nothing wrong with that kind of writing, or enjoying that style of reading. I do it often. The problem is when the series (for me) becomes stale, when the formula is so obvious that there's nothing surprising or new in the Recent Release.
Battle of the Labyrinth is edging close to that staleness (as you faithful readers know, I felt that way about Harry Potter, too). Even worse for Riordan, I'm not the only one that's noticed! One of my students said, "It was good, but 'meh'". Fairrosa said the same, only far more eloquently.
Yes, I'll read Book Five. But it's a good thing that Riordan's moving on to other books, other ideas. This one seems to me running out of steam.