After a brief prologue, Percy Jackson: Sea of Monsters opens on a whirling contraption of an obstacle course designed to be perilously difficult for teenagers (demigod or not) to climb. As the thing twirls and throws young challengers from its wooden handholds, it separates the weak from the strong, and the pitiless from the compassionate.

Thus five minutes into the movie we learn something about Percy Jackson, son of Poseidon, god of the sea, who gives up his place atop the vertical obstacle course to help save a fellow student from being dragged around and maybe mushed up by the thing's grinding gears. He's strong, compassionate, and willing to sacrifice himself for the sake of a friend.

Those character traits, which mirror a certain young wizard whose name is so synonymous with the sound of box office cash registers, carry leading boy-turned-man Logan Lerman through an adventure filled with opportunities for him to be both strong and compassionate. And thanks to some big fun set pieces, monsters, and timely cameos, Sea of Monsters nails the PG roller coaster experience director Thor Freudenthal was undoubtedly going for.

Unfortunately for the Percy franchise, audiences are very familiar with that aforementioned young wizard, and probably a few other similarly dispositioned Young Adult fiction heroes. And with its familiar character roles and fantastical creatures, Sea of Monsters never quite shakes the derivative feeling that comes with this territory. That's probably why no one was particularly surprised when the first movie came and went without much fanfare. The lukewarm response resulted in an awkward three-year gap between this movie and the last, giving the cast a little too much time to grow up and stop looking like teenagers.

Lerman in particular has bulked up, putting on the muscle appropriate for a 21-year-old actor set to play a WWII soldier alongside Brad Pitt and Shia LaBeouf in next year's Fury. It changes the tone of the character significantly from the 13-year-old boy in the books, but strict adherence to the source material doesn't seem nearly important here as it does in some adaptations.

That source material is routinely ironed into a more linear form as Percy and his band of fellow demigod teenagers track down the Golden Fleece, which will revive the tree that protects their sanctuary, Camp Half-Blood, from the forces of evil. And while Lerman gets to play the hero on this quest, the character actors are having the most fun.

Brandon T. Jackson returns to bring a silly kind of comic relief to the sequel as Grover, Percy's satyr friend who, like all satyrs, is preturnaturally drawn to the Fleece. Buffy the Vampire Slayer fans will enjoy seeing Anthony Stewart Head playing centaur camp counselor Chiron with a little more teacherly gravitas than Pierce Brosnan could bring to the role in the first movie. Ron Perlman voices ravenous cyclops Polyphemus, whom Percy and his friends must outsmart to capture the Fleece. Community's Yvette Nicole Brown pops up as one of the three Gray sisters to give Percy a timely ride. Stanley Tucci is aptly cast as Dionysus, known to the kids at Camp Half-Blood as "Mr. D," and perpetually depressed by a curse that forces him to go without wine. And best of all Nathan Fillion takes on the role of Hermes, the divine messenger, who runs an extraordinarily efficient UPS warehouse.

Sea of Monsters gracefully paces the action, so even unfamiliar moviegoers will be able to follow along. Those big flashy monsters and set pieces are spaced expertly apart so as never to overwhelm either the target audience or the parents brought along for the ride. And as for the book fans, they'll be pleased to see a key plot-point carried through in the third act. Not to mention Jake Abel, returning to the role of Luke Castellan, who has grown into a fair bit of evil eyecandy for the franchise's teen audience since the first movie.

Percy Jackson: Sea of Monsters isn't breaking new ground or getting in touch with any deep emotions, but as a PG popcorn movie, it hits its marks. See the Trailer below..