I love this book. A lot. It's one of the best children's books I've ever encountered - it's fast-paced, it's hilarious, it's full of amazing characters and it's set with an incredible premise. Best of all, it's not the least bit condescending: when I first read it, I learned a lot without feeling like I was going to school, and Riordan managed to explain everything to me without making me feel stupid, because let's face it, Percy didn't know even half as much mythology as I did.
Also, I absolutely love the chapter names. I've never found any other book/series that can make me laugh aloud by reading just the table of contents.
I can read and reread this book almost forever, and never get tired of it. In a hundred years it had better be on all of the classics shelves, or else.