The series is told in the first-person point of view that does slip into a epistolary every once in awhile. Where's the first couple books were aimed more towards young teenagers the writing ages along with the characters quite well. The consequences hit harder for the actions and situations that occur and the writing does feel to have a more added depth to it.
Still the story is primarily for young teenagers where the sequel series and the final book Phil's more appropriate for early y a genre. Meaning there's a little bit more romance and the adults are not always in the way. The series and the story maintains a good 5 star rating for the genre that it is in and for the way the story captures the reader and does nothing that really pulls them out.
I will say that coming back to the story after so many years and having read hundreds of books since I did catch something that pull me out just a little but given the age group in which the story is written is understandable. Without spoiling anything a certain character implies that there's really no more wild places on Earth and has been so for 2,000 or so years. In truth even today there are vast areas of undeveloped land. It made it feel very American, which I am, in the idea that there's no wild places. Well there vast areas development I would say there's more Wildland then man populated. I think the author was trying to convey a certain spirit but it did feel a tad bit preachy and logically as an older reader it did pull me out.
Still the story is impressive and how it tugs at the heartstrings and lays down the final foundation for the last book of the series. At time I do not know if Rick Riordan was planning on writing the sequel series but he had start writing other series based on pantheistic mythologies. And this story maintains it's cohesion while being entertaining and educational.