This was the book that made me glad that I waited for the series to end. The end of the previous book was a major cliffhanger, and if I had to wait for it, I would have been really agitated.
The story branched off in two directions. One was the path that Annabeth an Percy took. I really liked the emotional side of it. The hardship, the fight to stay together, and the people they meet there. I could see real character development in them, growing up. Especially Percy.
The rest of the group, who took the other route to the House of Hades, also did some growing up. Frank, I didn't pay much attention to before. However, in this book he came into his own. I loved Leo's story, and it was quite a surprise. I had forgotten about that part in the previous series. Hazel found new powers, and it was interesting how Piper and her could develop their own while working together. It was good to see that kind of cooperation between the two girls. Jason was more support in the story. He often went with the others on the small side quests that they had, but didn't seem to take the lead in any of them. Still, I would love to have him as a friend, he sounds like good support. Nico, I was so happy to have in the story. He had always been my favourite minor demigod, and I really didn't see the secret that was revealed about him. It made me very happy though, to have such a character in the series.
Overall, a really exciting book. It even felt longer than the previous ones. I did take longer to read it, but that was more about not having time to even sleep these past weeks, let alone read more than the page on the metro.
Cross-posted at http://unapologetic-reviews.blogspot.com, where you can find more reviews.