I started reading this series when the last book came out, The Battle at the Labyrinth, and I consider that the best of the run even after reading this one. This is a good book, but something was missing, even though it is action packed.
I liked the parts that tell you about the characters' backgrounds and history. The legends and myths were interesting, and the first couple books had more of that. There was a good amount of backstory in this book, but I still wanted more.
I think followers of Harry Potter will enjoy these books because of all the magic and legends. The world created in this series is not as defined as Potter's, but has it's own charm.