Evidently, Rick Riordan's "Percy Jackson" young-adult books haven't "broken through" with adults and older teens to the same degree that "Harry Potter" or even "Eragon" did (full-disclosure: I've not read them, myself) - otherwise I imagine it's movie adaptation would've been a bigger deal in the realm of movie-geek web buzz: Handily summarized as a more action-oriented "Potter" with Greek Mythology in place of witchcraft and playing out like mashup of Jonny Quest and "The Mighty Thor," (come to think of it... anyone following Marvel's Amadeus Cho/"Incredible Hercules" story would, I'm thinking, LOVE this) it's the sort of movie I can fully see myself considering "the coolest thing EVER" as a gradeschooler - as it is, I was shocked at how enjoyable I found it now. It's really solid fantasy/actioner, absolutely worth checking out especially if you've any fancy for repurposed Greek mythos.
Broadly, it's an "ordinary troubled boy is actually special" superhero origin-story. The basic idea is that the Olympian Gods (Zeus etc.) are still around and still in the habit of fooling around with mortals, frequently - as before - resulting in the birth of super-powered "demigods." Said demigods go about incognito, while the rest of the Hellenistic bestiary (minotaurs, titans, hydras... damn, but I LIVE for this stuff) slinks around on the margins of the "modern" world. As one-stop foundations for a "world of super-beings" go, I've heard worse.
Main character Percy Jackson happens to be the son of Poseidon, which makes him a gifted swimmer and able to telekinetically-manipulate water. That second part, along with his lineage, he's largely unaware of - to say nothing of how many people in his circle of friends and relations are secretly-magical helpers keeping an eye on him. He gets clued in as the plot steps on the gas: Someone stole Zeus' (Sean Bean) lightning bolt, which is the sort of thing that Wars of The Gods get started over. For some reason, Percy is suspect #1, so he has to get schooled in his true nature sooner than expected - spirited away to a summer camp dedicated to molding demigods into modern-day Hercules.
The plot contrives to send Percy and a pair of sidekicks on a fetch-quest to Hades, necessitating a magic object scavenger hunt through the various modern-day hangouts of mythic bad-guys. Kids (or adults, speaking for myself) familiar with the mythology in question are going to love these bits, since they'll catch the references earlier: One detour lands them in one of those chauncy roadside landscaping shops where you can buy tacky statues for the garden... lots of statues, come to think of it... Guess who. The cleverest - and most obscure - bit involves a Vegas casino, and feels like something Terry Gilliam would've popped into a Baron Munchausen sequel.
A big part of the charm is how - despite doing the Thor/80s-Fantasy-in-general thing of staging mythic dustups in modern urbania - defiantly "traditional" it treats the mythic stuff in the visual sense: The monsters all look (and "work") like they're generally supposed to, and there's no attempt to update or rationalize the Olympian Gods themselves - they appear as you'd expect: Giant-scale humanoids stomping around marble temples in togas and sandals. Even Zeus' bolt appears, literally, as a sparking shaft of lightning you can hold like a staff.
It does have most of the same problems that similar "trying to start a franchise" movies have, along with it's maddeningly silly full title "Percy Jackson & The Olympians: The Lightning Thief." Most of the non-main characters are forced to introduced themselves, explain their entire backstory, motivation, arc and then promptly excuse themselves with a casual wave of "bye for now, I'll probably be important two or three movies from now." But I will say that it's much less clumsy about this than, say, the first two "Potter's" (with whom it shares director Chris Columbus) were.
I'm not going to call it a rush-out-and-see sort of thing, but I dug it - and I'd definately be curious to see where it's all supposed to be going. I do have to wonder, though, if the makers of "Clash of The Titans" and "Thor" are at all annoyed that a bunch of their likely setpiece scenes and "big ideas" are already being done here...