Personally, this was my least favourite book in the Percy Jackson series. I've been thinking about why exactly, but haven't really found a reason. Perhaps I just read it at the wrong time, or too close on the other book so I was bothered with the repetitive structure of the story.
This time focussing on the story of the Labyrinth and Ariadna's wire, once again I liked the mythology. With the addition of some new characters it never stops adding new layers to the already complex mythology in the books. The story, while following the same structure of the other books, already felt like the set-up for the grand finale that's coming in the last book.
Still enjoyable though.
I read a Dutch translation of this book.