Yeah, the books aren't bad. I've read them all. Hell, I found them good enough to own.
Okay, here's the deal in the books:
All the demigods inherit something of their parents' domains. This really is where the movie pissed me off--all the people are the camp acted identical. The book's reflects the Greek Pantheon some--a wildly different bunch of people who argue a lot, but more or less live with each other. It also really lost a lot of the identity there.
The reason the children of Zeus, Hades, and Poseidon are...worrisome, is their fathers have quite a lot of power going, and some of it goes down to their kids.
So, while Percy has a good variety of teh Superpowers relating to water, the movie handles them considerably less well than the books. He's also a lot more entertaining in the books. The guy in the movie is a lot more of straight man, where in the books...well, none of Percy's crew has their head on completely straight.
Also, the plot was really butchered. I have no idea how they're going to fit Kronos in, since he should have been introduced pretty close to the start.
It helps the books don't take themselves seriously. I mean, here's the official art for Poseidon in Percy Jackson:
http://www.rickriordan.com/wp-content/u ... seidon.gif
He really does show up, in the text, in clothes like that. And in Bermuda shorts and sandals. His throne looks like a deep-sea fisherman's swivel chair.
Hades complains about how the population explosion has forced him to keep expanding the Underworld (which, by the way, isn't portrayed as straight Hell. it makes a point to describe the three different areas).
Ares tends to go around looking like a biker because he gets a kick out of it.
The movie took a lot of the goofing around out of the books, and therefore, a lot of fun/redeeming value.