Fulfilling just a fraction of J.R.R. Tolkien’s “There and Back Again” subtitle, “The Hobbit” alternately rewards and abuses auds’ appetite for all things Middle-earth. While Peter Jackson’s prequel to “The Lord of the Rings” delivers more of what made his earlier trilogy so compelling — colorful characters on an epic quest amid stunning New Zealand scenery — it doesn’t offer nearly enough novelty to justify the three-film, nine-hour treatment, at least on the basis of this overlong first installment, dubbed “An Unexpected Journey.” The primary advance here is technical, as Jackson shoots in high-frame-rate 3D, an innovation that improves motion at the expense of visual elegance.

Though international B.O. success seems all but assured for a franchise that has already commanded nearly $3 billion in worldwide grosses, splitting the source material into multiple pics here mimics a frustrating trend among lucrative fantasy adaptations, from the two final “Harry Potter” films to the bifurcated “Twilight Saga” finale, stringing fans along with incomplete narratives. Whereas “The Lord of the Rings” naturally divided into the three books, “The Hobbit” contains scarcely enough story to support a single feature, as those who recall Rankin/Bass’ 1977 animated made-for-TV version know all too well.

Tolkien’s delightful yet easier-going novel, written with young readers in mind, recounts the relatively simple tale of how Bilbo Baggins (“The Office’s” Martin Freeman, affable as ever) traveled with dwarves to face the dragon Smaug and, in so doing, came to acquire the fabled ring.

A mythologically dense, CG-heavy prologue details how Smaug raided the dwarf stronghold of Erebor, taking possession of the Arkenstone, a glowing gem of ambiguous power. Conjured by Jackson and returning co-writers Fran Walsh and Philippa Boyens (credited along with Guillermo del Toro, who at one point planned to direct) for the sake of spectacle, this unnecessary pre-title sequence recalls setpieces from the second and third “Lord of the Rings” movies, as if to assure fans they can expect more of the same — and sure enough, “The Hobbit” offers familiar run-ins with orcs, trolls, goblins and even Gollum before interrupting the adventure halfway to its destination, the Lonely Mountain, to make room for the next installment.

But Bilbo’s “unexpected journey” is awfully slow to start. The film first locates him in Bag End, the cozy home in the Shire where the eleventy-one-year-old halfling hero (played briefly by Ian Holm and accompanied by Elijah Wood’s Frodo) narrates the adventure that first brought Hobbits into the affairs of Middle-earth’s more bellicose species. That tale begins six decades earlier, when the wizard Gandalf (Ian McKellen) appears with a challenge for the younger Bilbo (Freeman), leaving a magic sign that brings a swarm of dwarves to the reluctant hero’s door.

With names like Balin and Dwalin (Ken Stott and Graham McTavish), Oin and Gloin (John Callen and Peter Hambleton) and Fili and Kili (Dean O’Gorman and Aidan Turner), the 13 dwarves are virtually indistinguishable apart from their facial hair — though one needn’t be Galadriel (Cate Blanchett’s future-seeing Elf queen) to recognize O’Gorman as a Kiwi heartthrob in the offing. In the absence of clearly defined characteristics, the unwieldy lot make Snow White’s companions seem downright three-dimensional.

Speaking of 3D, the technique adds a level of dynamism to Andrew Lesnie’s swooping camerawork, which once again cuts from the closest of closeups to the widest of wide shots, in addition to plunging down and around elaborate enemy encampments, such as the underground Goblin-town, where spindly rope bridges teeter over gaping chasms. But 3D also complicates the forced-perspective tricks Jackson used in the earlier films, making for odd, eye-boggling moments, especially in the crowded Bag End scene, where Gandalf somewhat unconvincingly towers among characters half his size.

More disconcerting is the introduction of the film’s 48-frames-per-second digital cinematography, which solves the inherent stuttering effect of celluloid that occurs whenever a camera pans or horizontal movement crosses the frame — but at too great a cost. Consequently, everything takes on an overblown, artificial quality in which the phoniness of the sets and costumes becomes obvious, while well-lit areas bleed into their surroundings, like watching a high-end homemovie. (A standard 24fps projection seems to correct this effect in the alternate version of the film being offered to some theaters, but sacrifices the smoother motion seen in action scenes and flyover landscape shots.)

After Bilbo finally accepts his calling 40 minutes into the picture, such technical distractions virtually disappear as Jackson draws auds into his familiar world, particularly a troll-infested forest and the film’s darker, more expressionistic realms. Recognizing the limitations of their source material, Jackson and his co-writers pilfer freely from Tolkien’s other writings, including appendices to “Lord of the Rings” that reveal such details as where Gandalf goes during his long disappearances.

With few exceptions, these insights bog down a tale already overtaxed by a surfeit of characters. The film introduces Radagast (Sylvester McCoy), a comical brown wizard with an ordure-streaked beard, and an unsatisfying subplot involving a Necromancer that’s clearly an early form of Sauron, out of place in this story. It also makes room for cumbersome reunions — or “preunions,” perhaps — with Galadriel, Elrond (Hugo Weaving) and Saruman (Christopher Lee) in the elf city of Rivendell, hinting at the greater roles they will play in “The Lord of the Rings.”

The pic stands on firmer footing when embellishing the book’s more cinematic sequences into full-blown setpieces, such as a perilous cliffside passage complicated by the fact the mountains themselves appear to be doing battle, like giant stone Transformers. An expanded subplot pitting dwarf captain Thorin (Richard Armitage, nobly trying to match Viggo Mortensen’s smolder) against a battle-scarred and vengeance-bent orc helps disguise the fact that this particular road trip has no immediate villain.

Still, Jackson and his team seem compelled to flesh out the world of their earlier trilogy in scenes that would be better left to extended-edition DVDs (or omitted entirely), all but failing to set up a compelling reason for fans to return for the second installment. The film hints at a looming run-in with Smaug, but makes clear that this mission serves more to win back the dwarves’ lost kingdom than to protect the fate of Middle-earth. Bilbo’s arc, therefore, consists of proving his value to a mission that doesn’t concern him personally.

In keeping with the child-friendly tone of the source book, “The Hobbit” is more comical, features a couple of amusing songs, and doesn’t dally on funerals the way “The Lord of the Rings” did. But it’s no kinder on small bladders or impressionable eyes, running every bit as long and violent as Jackson’s initial trilogy.

While it would have been fascinating to see del Toro’s take on “The Hobbit,” there’s something to be said for continuity. Few film series have achieved the consistency of look and feel maintained across these Middle-earth-set stories, and once the adventure gets going, Jackson reminds auds of his expertise at managing action on a scale that would have made David Lean wish he’d had CGI in his toolbox.

That connection is clearest in the character of Gollum, once again performed by Andy Serkis, who loses not only an unmistakably schizophrenic game of riddles to Bilbo, but also his precious ring. Below-the-line contributions, including those of composer Howard Shore and the entire production and costume design teams, support the illusion that we never left Middle-earth.