The main reason this book was so good was because there was so much character development! Percy and Annabeth developed together, Frank became worthy of himself, we finally figured Jason out, Hazel and Piper finally figured themselves out, and Leo and Nico... Well, I'm getting to that next.
This is where the spoilers kick in, so don't read on if you haven't read the book, please.
The halfway point of the book may just be one of the best scenes in YA literature. It's Nico's scene, and it lets us discover him, and Jason as well. This is the Cupid scene, the scene in which everything about Nico finally clicks into place: he has (or had, if you believe Nico, which I most certainly do not) a crush on Percy. Every single thing Nico has ever done or said - especially around Percy - finally makes sense. It all takes on a new meaning, and you understand him so much more. I loved this scene too because it shows us something we needed to see: even in books written for middle schoolers, gay people are okay. Rick took a character we all knew and sort of loved, and gave him new depth, in the form of a controversial topic in the world today, and I'm so proud of him for it. He may lose some fans. He was totally reading our fan fiction. But it was the best thing I have ever read.
The second scene that just made the book for me was Leo's time with Calypso. I'll admit that I used to kind of ship them, but then I decided they'd never meet and that they probably wouldn't like each other anyway. But ohhh man… I was soooo wrong. Leo and Calypso is my new OTP, and it is the most beautiful thing of all - they hated each other at first, and it seemed like a major setback, then a tragic love story. I think we all know what the oath to keep with a final breath is now: "I'm coming back for you, Calypso," he said to the night wind. "I swear it on the River Styx."
I don't care what the rest of you think, but Leo NEEDS to get back to Ogygia.