First of all, I didn't like the Idea of a civilization's fate being in the hands of twelve years old boy. That made the whole story look stupid to me.
On the other hand, I kind of hoped that the villains would somehow manage to destroy the the western civilization. It really bothered me that the writer talked about western civilization in a way that it's such a sacred thing.
The plot was loose and stupid. (Protagonists tended to accidentally get into some monster's shop and found the next clue there.)
But it was a nice way to get familiar with Greek mythology. I'm about to start reading Homer's Iliad and the Odyssey.
The only character I liked was Thalia, who appeared briefly in a dream.