The House of Hades - Rick Riordan
Great moments, ok book.
Spoilery review in private; will move to this space once have laptop to add spoiler tags.

ETA: Love Percy&Annabeth, Leo&Calypso - Leo told her about his private, secret dream to open a shop, and they dream of working it together, making it a joint effort. I love them. The couple's journey through Tartarus was arduous and long. It was honestly annoying. Frank's "growth spurt" was interesting, but I only understood it after. Hazel controlling the Mist is cool, but that I didn't understand at all. Hecate's unpredictability, I like. No allegiance to any of the demigod children on the quest, whoo!! Jason is learning to be a big brother figure, and gaining his footing.

There was more I wanted to say, once upon a time, but I've forgotten it now =(