It’s difficult to find a children’s fantasy novel without “For fans of Harry Potter” (or the more threatening “Step aside, Potter”) among the critic’s notes on the back cover. Living in a post-Rowling generation is a double-edged sword for authors whose talent lies in spinning heroic tales with a heavy dose of mythology. The market for this particular genre is certainly larger than before, but the bar is set high at Harry Potter, and he killed Voldemort. Standing out from the pack is a monumental achievement (insert your own “Herculean” pun), and author Rick Riordan’s Percy Jackson novels, which follow the lives of the sons and daughters of ancient Greek gods, stood out enough to merit a film adaptation. And so, Chris Columbus, who helmed Harry Potter and the Sorcerer’s Stone and Harry Potter and the Chamber of Secrets directs Percy Jackson & the Olympians: The Lightning Thief -- a natural, albeit ironic choice. The plot offers a soapy, present-day twist on a very old mythos: Ancient Greek gods descend to earth on occasion, where they inevitably find a pretty young woman to distract them from the demands of god-hood, and whom they just as inevitably impregnate. Their progeny -- half-god, half-human hybrids known as demigods -- must fend for themselves on earth, and hone their more godlike qualities at a secure (from monsters) location known as Camp Half-Blood. The demigods we care about are Percy Jackson (Logan Lerman), son of Poseidon, God of the Sea; Annabeth Chase (Alexandra Daddario), daughter of Athena, Goddess of Wisdom; and wisecracking satyr Grover Underwood (Brandon T. Jackson). Their quest takes them across the United States, through the Underworld, all the way up to Mt. Olympus, where they must either return Zeus’ stolen lightning bolt, or convince him that Percy is not the thief. The film has its share of flaws, most of them typical for children’s fantasy movies. The first half is quite clumsy, and with no internal dialogue the characters’ feelings are difficult to gauge. The one-liners (virtually all delivered by Brandon T. Jackson) have a forced quality about them -- setup, pause, punch line, rim shot -- and the action scenes have a tendency to start too abruptly and last a little too long. There are, however, a lot of good things to say about Percy Jackson & the Olympians: The Lightning Thief. The elder characters are a lot of fun to watch, particularly Pierce Brosnan, who plays the role of a centaur so naturally it’s hard to remember that he’s not half-horse in real life, and Uma Thurman as a modernized Medusa with a perfectly coiffed head of snakes (sadly, not black mambas) and a corseted leather jacket that adds to the sense that the young heroes have accidentally stumbled upon the unholy union of a dominatrix and Renaissance festival. Steve Coogan and Rosario Dawson (king and queen of the Underworld, respectively) act exactly the way you’d expect an old married couple to act after spending an eternity with only each other for company, in Hell. The younger actors are also very good -- certainly better than the Potter kids were in Sorcerer’s Stone -- but their dialogue is almost slavishly dedicated to setting up the attraction between Percy and Annabeth for future movies, which is too bad, because when they get to act in this movie, they shine -- particularly Brandon T. Jackson, who is capable of so much more than comic relief. The film also looks as fantastical as its story, each set topping the last until the Underworld, with its fiery lakes and slowly traveling airborne debris (“the discarded scraps of humanity”), takes the prize. Overall, while not spectacular, Percy Jackson & the Olympians: The Lightning Thief has the magic, the energy, and the heart to become a really fun standalone fantasy adventure series for ’tweens.