"The Polar Express" is the world's first inter-species Christmas movie. The characters aren't exactly animated — the human actors who hunker at their cores supply their very humanesque movements and facial expressions. But of course they're not exactly "human," either — with their overlays of computer-generated digitalia, they look like real people who've been dipped in liquid vinyl. Obviously, the makers of this $165-million film were going for magic and wonder — and in some ways it is magical and wondrous. But upon close contemplation of the characters here, with their smooth, doll-like skin and count-every-strand hair, another word creeps into mind: eerie. Which is a different thing.

The movie is based on writer and artist Chris Van Allsburg's 1985 illustrated book, "The Polar Express," which has become a classic of modern kid-lit. (His 1981 book, "Jumanji," was also made into a movie, a 1995 CGI spectacular starring Robin Williams.) The story is a winsome fantasy. Late one Christmas Eve, a young boy is roused from his bed by a sound of great huffing and chugging outside. Looking down into the snow-covered suburban street, he sees that a train has pulled up in front of his house. Tiptoeing out the front door, he watches a uniformed conductor climb down from one of the cars and beckon him over. Consulting a list, the conductor tells the boy that it's been noticed that he hasn't sent a letter to Santa this year, and that he's even left the task of setting out milk and cookies for him to his younger sister. With an air of mild disappointment, the conductor, a gruff but twinkly man who looks almost exactly like Tom Hanks, tells the boy, "If I were you, I'd get on board."

The train is the Polar Express, and every year it makes its Christmas Eve rounds, picking up children whose faith in Santa is wavering and transporting them to the North Pole, where Santa himself will restore it. Inside the train are many other kids, who, like the new arrival ("Hero Boy," he's called in the movie's production notes; none of the characters has an actual name), are all in their pajamas. The three other characters we come to know best here are childhood archetypes: Hero Girl, Lonely Boy and Know-It-All Boy. With the fussy conductor presiding, their adventure begins.

This is an action movie, and the action is pretty much nonstop. We follow the train as it barrels down into "Glacier Gulch" — a wild roller-coaster ride — and fishtails out onto a vast frozen lake, whose ice soon begins to shudder and crack. We tear along behind a pack of yowling wolves as they bound through the moonlit drifts. (The "camera angles" in these scenes are so impossible, but seem so real, that we can only respond to them with real astonishment.) And in one marvelous extended sequence, we follow a lost train ticket as it flies out a window and flutters through the snowy night until it's scooped up by a passing eagle, who wings off to her nest with it, but then loses her grip, relinquishing it once again to the winter wind, which carries it flittering back toward the railroad tracks and, finally, back into the train, which has just come roaring around a bend.

The Polar Express finally winds its way up an Alp-like mountain to the North Pole, an oddly modern metropolis glimmering under gorgeous curtains of Northern Light. Here, regiments of elves scamper around warehouses full of toys, selecting presents for Santa's gigantic gift bag while banks of television monitors display the pillow-bound faces of sleeping children all over the world. Many more adventures unfold for the Polar Express kids, along with more visual wonders for the audience (like the uncannily detailed reflections on the surface of a small silver sleigh bell rolling across a cobbled street). But then Santa finally appears, making a rock-star entrance in a blaze of white light, and something at the heart of the movie goes completely off. Because "Mr. C" (as he's called) is weirdly slim and belly-less, and with his pale, polished digital skin, he looks as if he's had a face-lift. He's the crowning fake in a procession of weirdly hybrid impostures.

Motion-capture technology — the animation technique in which actors wearing reflective dots all over their bodies can be tracked by computers and turned into minutely mimetic synthetic characters — is no longer novel. It was used to disquieting effect in the 2001 film "Final Fantasy: The Spirits Within," and of course it was unforgettably employed in creating the fantastical character of Gollum in the "Lord of the Rings" movies — still the "mocap" platinum standard. But Gollum was a seamless invention, and as a wholly imaginary creature with no real-world analogue, he was uniquely believable. In "Polar Express," the human substance within the "animated" characters is clearly visible. The conductor could only be Tom Hanks; and the other characters could only be real actors with digital carapaces fitted over their merely human bodies. But why is this being done? I think the motion-capture technique, so amazing only a few years ago, can only yield diminishing returns of amazement. It hasn't been perfected yet (thus the unmistakable human residue glinting creepily beneath the bland surfaces of the "Polar Express" characters), but when it is, what will we have: a new "reality" that's indistinguishable from the reality we already know? What would be the point of that, exactly? In this technical respect, at least, "Polar Express" seems like a train to nowhere.