I was in the biggest reading slump whilst reading this, so this review won't be as objective as usual. =D 
 The good stuff 
 1 - Percy and his sass are back. His chapters were definitely the best! 
 2 - Frank and Hazel are much more interesting than Jason and Piper 
 3 - That reveal at the end about Leo (OH MY GOOOD) and the anticipation of Percy finally reuniting with his Camp Half-Blood friends 
 4 - The Amazons, god, they're so intense and badass (also Amazon Headquarters... LOL) 
 5 - Frank's Gift and family history (I love granny Zhang) 
 6 - Hazel's powers and her bond with Nico 
 The bad stuff 
 1 - it felt too long, at least 100+ pages were dispensable 
 2 - it felt too predictable (except for the reveal about Leo), the whole thing about freeing death and fighting the giants... The outcome was clear! 
 3 - in general I'm not sure if this extension of Percy Jackson & the Olympians is really necessary, it doesn't add anything really 
 4 - I wish Riordan would write more about the Roman Gods and the mythology, I always like these parts the most