The Son of Neptune is the sequel to the The Lost Hero which is the start of the series that is the sequel series to The Percy Jackson Series, all by Rick Riordan. I like how he started off the series with a whole new set of characters instead of going straight to Percy's story because it created more of a mystery of what happened to him and why everyone's looking for him. This brought a lot of things into the story line that made it more enjoyable to read. He changed much about the story by throwing in Roman mythology as well as Greek mythology.
The new characters that Rick Riordan introduces are Leo, Piper, Hazel, Frank, and Jason. All of them except Jason each play a part in helping either Percy or Jason try to regain their lost memories, get them back to where they belong, and to stop Mother Nature herself, Gaea, from destroying the world and the gods. Each of the characters goes through some emotional drama with their parents, each other, and even themselves. Some don't know how to control their powers, some fall in love with each other, and some are angry at their parents for what they did to them, giving them dangerous powers and not helping them in their lives.
The new thought-provoking aspects of the books make you have to remember who is who. You have to remember who the Greek Gods are as Roman Gods and vice-versa because they use both names through out the book and it make you have to go back in the book to see who they were talking about. They also mention names later in the book that they might not have mentioned since the beginning of the book, making you re-read that part so you aren't confused. These really made reading the book a lot more enjoyable for me with all the brain work going on (if you didn't know, I'm always doing something in my head that retains to before).
The Roman mythology that is put in to this book, like I said before, made the book a lot more complicated with the references to Romans and even some new Greek references that haven't been used in his books before. This gave me a little more understanding of a Roman, Greek relationship throughout the books that work in real life. This was kind of like a history lesson tied in with the fun of reading. The author's use of the mythology and terms were very accurate and if you don't believe me, go look for yourself.
I would strongly recommend you read this book, it's just amazing.
