I only started this because of the movie--hadn't heard of it before, and even though it is clearly aimed at younger teens still found it enjoyable. I took a lot of Latin in high school and always enjoyed reading Greek and Roman mythology so really was intrigued by all the ways the author worked that in. There's even a Trojan war reference --a parallel to Achilles sulking in his tent and coming back to the fight when Patroclus dies. Definitely would recommend it to late grade school or junior high readers, but it's fun for older people as well.
I've now ripped through all 5 books I see on Kindle. Although those do resolve the major issues I sensed the ending left it a bit open for more books--anyone know if more are planned?
PS There's a lot of fighting, and "good" characters do die (the bad ones just vaporize), but no sex beyond a G rated kiss. It's even something you could read aloud with younger kids. I read Greek myths to/with mine who loved them (well, not the general unfairness of the gods, but the stories), and since they had some background they would have loved these as well.