I had read the original series, and I love it...I would choose both Percy and Harry Potter, for my top 10 fantasy series.
I had wanted to see the movie when it was in theaters, but it went out, so I'd waited 'til it came out on DVD. I'd watched it and I thought it was really awesome; I did not like some of the negativity on it. The film (as you all know), is about teenage Percy Jackson who seem to be an ordinary teen; until after a monster attack at the museum (a Fury disguised in his English teacher), he found out he is a son of the sea god Poseidon. And have been accused of stealing Zeus' master lightning bolt, he finds himself caught between angry and battling gods, he and his friends embark on a cross-country adventure to catch the true lightning thief, save his mom, and unravel a mystery more powerful than the gods themselves.
So anyway I really love this film; even if there were changes to the characters.