One of the problems I had was the number of new characters to keep track of in this book. Thalia joins Grover, Percy, and Annabeth in rescuing Nico and Bianca di Angelo from a Manticore. Along with many bad guys, we meet Atlas and the goddesses Athena, Aphrodite, and Artemis. We also meet Artemis' hunters, Annabeth's dad, Zoe Nightshade, and Rachel Elizabeth Dare. Thalia, Bianca, and Zoe seemed too much alike and I kept getting them confused. With so many new characters, I didn't get attached to anyone like I did in the other two books.
The quest seemed contrived and I didn't feel the urgency for everyone to make it safely to Mount Othrys. It also seemed redundant to keep using the solstice as the deadline they faced.
I did not like the Pegasi and that was disappointing because they are some of my favorite mythological creatures. I did not like the way Blackie talked in slang that seemed to mimic stereotyped versions of African American speak. Mr. Riordan could have done a much better job of creating the dialogue for them. I felt the same way about Percy calling the Ophiotaurus "Bessie."
I liked the ending surprise. It fit well with the details in the book and made a surprising shock that I didn't see coming. I am excited to see how Nico fits into the prophecy in the next book.
It was an okay book, but not as great as the first two in the series.