A visual marvel that’s unfortunately pretty derivative in terms of plotting, this animated 3D adventure from Blue Sky Films, the makers of the “Ice Age” series, is appealing enough overall to amuse both kids and the adults who watch it along with them but not sufficiently entrancing to become a franchise-spawning classic.

Like any number of children’s pictures—most recently “The Secret World of Arietty”—it’s about little folk, in this case two groups of forest dwellers. One is made up of the Leaf Men, the hummingbird-riding army of archers who use their bows and arrows to guard the Forest Queen, Tara (voiced by Beyonce Knowles), the source of all that’s green and growing—a whole community of anthropomorphized plants sand tiny critters. The other is their dark opposite, the Boggans—grotesque, rat-like creatures led by the evil Mandrake (Christoph Waltz), who wants to dethrone Tara and turn the woods into a bleak, desiccated wasteland. (They’re also called Rotters, for the rot they bring, and they travel around on bats.) Check the ecologically correct message off the to-do list! On the other side of the size spectrum is teenager MK (Amanda Seyfried), who’s arriving at the isolated house of her father Professor Bomba (Jason Sudeikis), a goofy Andy Dick lookalike. He’s been obsessively searching for the little folk for years—a passion that estranged him from his recently-deceased wife. Ah, the parental-child re-bonding element of the plot clicks in!

The two worlds come together when Tara ventures from her protected perch to select a bulb that will become the heir to her powers. Unfortunately, her dalliance outdoors is taken by Mandrake as the opportunity for a surprise attack, and in the ensuing melee her devoted general Ronin (Colin Farrell) cannot save her. She is, however, able to pass along the chosen bulb to MK, who for some unexplained reason has been shrunk to the little folks’ size. She’ll eventually become prize sought by Mandrake but defended by Ronin and rebellious young Nod (Josh Hutcherson), the orphan son of the general’s best friend but a lad who can’t follow order and has gone AWOL to race in the flying contests run by a mobster toad (Pitbull). Their mission is to take her to the domain of the caterpillar (Steven Tyler) who’s the guardian of the community history and can help determine how to induce the bulb to flower and transmit Tara’s powers to another and save their world. Along the way, of course, MK and Nod—initially hostile though they may be—become gooey-eyed over one another; check off the “teen romance” category!

And one can’t forget the slug named Mug (Aziz Answari) and a snail called Grub (Chris O’Dowd), who as the guardians of the bulbs accompany Ronin, Nod and MK on their journey. Mug, a romantic sort, sees himself as Nod’s rival for MK’s affections, while Grub dreams of becoming a Leaf Warrior himself, while they also bicker between themselves. They fill the traditional Disney role of cute slapstick sidekicks. (There’s also Professor Bomba’s three-legged dog, whose antics fall into the same category.)

Needless to say, the story—inspired by, though not directly adapted from, the children’s book “The Leaf Men and the Brave Good Bugs” by William Joyce, who also served as one of five screenwriters—must end in a big confrontation between the heroes and Mandrake’s forces over whether the bulb will be used to revivify the forest or kill it. The outcome is never in doubt, though the screenplay tosses in hurdle after hurdle to try to generate suspense about it. Fortunately not only are Ronin and Nod indefatigable, but MK can enlist a giant—her dad—to intervene on their behalf. In the process, of course, Bomba is finally introduced to the miniscule species he’s been seeking for years—check off the “dream fulfilled” slot!

“Epic” is obviously pretty formulaic, but it manages to orchestrate the predictable elements with enough panache to keep things reasonably fresh, and it’s beautifully crafted, giving a degree of shimmering elegance to the backgrounds, whether they be the green ones of the leafy world or the grays of the rotting one. And the obligatory 3D is applied with more sophistication than usual. The character animation is generally first-class, though Ronin seems a fairly generic fellow and Tara is frankly a regal bore, and the voice work is solid, even if Beyonce’s contribution is bland. Danny Elfman’s score complements the visuals well enough, though it employs his characteristic ticks a bit too insistently.

And apart from Mub the slug’s trail of ooze, the picture happily avoids the penchant for mild grossness that seems to afflict children’s movies nowadays. That’s reason enough to put it head and shoulders above most of the competition, despite the Leaf Men’s diminutive size.