I enjoyed this film although I didn't really expect to as I used to hate "myth themed" films on TV. The characters are well acted, especially Percy himself. The plot is good, with lots of references to my classical studies lessons, recently revisted whilst helping son with prep!
I had read it was a Harry Potter rip off - it is not at all. It is completely different although just as good. Instead of witches and evil we have Gods and mortals, less sinister yet just as entertaining. Yes, Percy becomes a teenager before learning his father is a "top 3" God but, unlike Harry, his parents are both still alive & rooting for him.
It could be quite awful though and I have to say that the quality of the acting carries it off for me. The special effects are pretty good too.