I just finished the 5th and final book in the series (at least the first series - there's a hint that other series may be in store) a few days ago and saw the movie on opening night.
First, here are some notes on the books that I wrote in response to a question from a friend:
The books are a little tricky in spots (because they are Greek myths after all), but I think they're okay for 12 and up - maybe younger depending... John and I and Ria have all read and talked about the first five books - and I recently read D'Aulaire aloud to all of the kids (the books are less weird and much more enjoyable if you're familiar with the myths first), so now John is starting to read Percy Jackson aloud to the family. Terri (age 12) is pushing ahead on her own.
There are a few little things that made me cringe (not all that nuts about the oracle thing, for example, particularly in the last book) but liked them on the whole. There are a number of little things that may be bothersomely sensitive to particular families or particular children, but on the whole there were more things that I liked than didn't like - and some of these were *really* great.
Next the movie:
I give the movie two thumbs down. It takes the prize as the worst adaptation of a book that I've ever seen - and I usually enjoy adaptations, even if they're a bit off. This was a totally different story.
I found the books to be a rather fun cross between Greek Mythology and the Phantom Tollbooth (or something like that). Not perfect, but clever and thoughtful in many ways. The "Phantom Tollbooth" aspect was completely lost in the movie which instead went for more of a "Clash of the Titans" feel.
Basically, the movie takes the story way too seriously.
By the way, Decent Films has a pretty good review of the movie here. It's really too bad, because many of the criticisms that apply to the movie don't apply to the books.
I'm posting more details about the movie in the comments box. Don't read it if you want to avoid spoilers!!!