I went and saw Percy Jackson and the Olympians: The Lightening Thief the other day. (Thank goodness for $5 Tuesdays!)
The short: don't see this movie. It's not very good.
I know I'm biased since I enjoy the books, but it's really not good.
It's hard for me to write why I didn't like the movie without going into why I like the book so much. I guess, essentially, they took out most of the stuff that I really enjoyed about the book when they made the movie. They took away the mystery of the camp. They took away Percy's journey of self discovery. They took away his best ally and mixed her character with an antagonist. They made the pettiness of the gods less petty more and epic. They took away the oracle and its prophecies. They took away the gifts from parents. They didn't have blue cookies.
And what they did have wasn't very good. The special effects didn't look good. The creatures didn't look like they were in the world of the film. The camp was there, but it was more of a training ground than a camp/home for the kids. Medusa was boring. Hades's realm looked more like the Christian version of Hell rather than, you know, the misty world of the dead.
There's so much more. I don't want to think about it.
Just don't see the movie. Trust me.