Beowulf (voiced by Ray Winstone) prepares for a harrowing battle with Grendel in the digitally animated Beowulf.

“Beowulf” reinterprets the English language’s oldest narrative through the latest techniques of digital filmmaking. The results are a sometimes spectacular, often empty spectacle.

The 8th-century poem isn’t the stuff of traditional screenplay structure – it’s two hero vs. monster battles separated by a 50-year gap – and despite an ingenious adaptation by fantasy novelist Neil Gaiman and Oscar-winning screenwriter Roger Avary (“Pulp Fiction”), the tale feels a bit garbled.

You watch it with a sense that there are still scenes missing. The computer-generated visuals, based on motion-captured performances by the cast, are at once photorealistic (you can count the whiskers in Beowulf’s blond beard) and phantasmagorical. (The monster Grendel is an 11-foot-tall fetus/corpse/lutefisk thing.) The film will have a wide release in 3-D, and that’s definitely the format it was meant to be seen in.

As you may recall from Cliff’s Notes, boozy old King Hrothgar of Denmark (Anthony Hopkins, rendered in eerie living-mannequin style) needs a hero. Grendel, a giant mountain troll, breaks up his parties, bursting into the great hall and gobbling up members of the royal court with very poor table manners. His reluctant consort, Queen Wealtheow (Robin Wright-Penn), wouldn’t mind meeting a champion, either. Enter the Viking Beowulf (voice by Ray Winstone, body a digital amalgam of Sean Bean and Hulk Hogan), a fabled warrior who claims to have slain aquatic monstrosities and swum for a week against tidal wave seas. He’s a hero with flaws of vanity and braggadocio as overblown as his physique.

From the moment he bellows “I am Beowulf, and I am here to slay your monster!” he upsets the balance of power in the kingdom. Unferth (John Malkovich), a conniving courtier, resents the newcomer, while Wealtheow can scarcely catch her breath in his presence.

The film makes quite an issue out of Beowulf’s superhero physique. As he strips down for the night, the camera virtually licks his body, while comic-prudish Austin Powers obstructions hide his broadsword. There’s plenty of raucous, politically incorrect humor in this retelling.

Beowulf proves he’s more than good looks, and when Grendel attacks again, he mortally wounds the beast with his bare hands in a scene of exuberant bloodletting. After that confrontation he tracks the creature back to its lair, determined to kill its mother. When she turns out to be a shape-shifter who can do a striking impersonation of Angelina Jolie, his commitment wobbles, and he makes a decision that will return to haunt him after he assumes the king’s throne.

Where the film works best is in the reinvention of the narrative. The hero-good/monster-bad flatness of the poem is reworked for modern sensibilities, with flawed characters who grow through their experiences. Grendel (harrowingly portrayed by Crispin Glover) is a pitiable ogre whose life is near-constant torment. His ghastly mutant form is cleverly accounted for, as is his angry yet fearful relationship with Hrothgar.

The origins of the mysterious dragon are made clear, too. These monsters are byproducts of the kings’ lust, power or lust for power, demons that are not so easily vanquished.

Director Robert Zemeckis has succeeded in making his human characters much more plausible than in his choo-choo-of-the-undead picture “The Polar Express.” The skin textures are remarkable, muscles knot and relax realistically, and the eyes are full of emotion (at least for the primary male characters and Jolie; the background folks aren’t so lovingly rendered).

His action scenes are borderline ludicrous, however. He seems drunk on the novelty of his new toys, using them to dazzle more than to advance the story.

Zemeckis sends his virtual camera zooming up to the skies along the trajectories of flung bodies, and dollying back from a castle window up to the top of a far-off mountain (mountains in Denmark?) just because it looks cool. From the look of the movie, he shot every wild idea that came to him without regard to the flow or development of the images. Then he chopped it up, slapped it together with his fingers crossed, and hoped everyone would be too giddy to notice the holes.

There are passages of exuberant fun when the flying dragon tries to char-broil the ladies of the court while Beowulf holds on with one hand and hacks with the other. The overall effect is intrusive and gimmicky. A collage of interesting fragments, “Beowulf” is a triumphant mess.