You may not know it, but this picturesque tale by Chris Van Allsburg (who also wrote the book of Jumanji) is now the set text for preaching the 'real meaning' of Christmas for massed ranks of American parents afraid their children might grow up. It's their Snowman, bedecked with beautiful oil-paintings of a world forever poised on the cusp of the big day - magical, sprawling images of an American wilderness both unknown and comforting.
Accompanied once again by Tom Hanks, his compatriot in reinforcing the study values of traditional Americana, Robert Zemeckis has set out to transform those lavish pages into a digitally-rendered family movie. Expanding on the thin tale (it's barely 15 pages long) by stoking the boiler of action and spinning out the visual opportunities with an honest care for the book, this is a sackful of twee, seasonal conformity delivered with rapturous thrill - a film that's both sentimental and extraordinary.
There is some dispute over whether it's exactly an animated film. All the performances are real, scanned in and relayed into rich CGI, care of a Gollum-style hi-tech formula. Hanks, in a blue leotard smothered in digital sensors, acted no fewer than five of the major roles (including the kid and, most obviously, a wry ticket inspector given his own puddingy looks) on soundstages, granting the characters genuine human movement and expression, albeit more doll-like than photorealistic. The camera moves, too, are devised as if real, functioning to the natural tilt-and-pan of humble analogue technology.
Yet all else is struck from Zemeckis and his designers' imaginations, and they touch heights of splendour not even reached by Pixar's zanier moments. The sense of the train's hurtling motion is perfection itself, with its white-knuckle plunges over impossible inclines (you've got to try it in IMAX 3D - it bends your brain). In a gentle Forrest Gump riff, a lost ticket is blown like a feather from a window to make a solo journey across wolf-haunted woodlands and icy drifts, before, miraculously, returning to the locomotive. It is the single most lyrical passage of CGI yet painted on a screen, a reminder that art and pixels are not mutually exclusive.
There's a tinge of irony in the application of this new-fangled technology, considering how it's been used to recreate an old-fashioned America via dreamscapes dripping in nostalgia. With Sky Captain, it was a mythical '30s spooked up with the shadowy licks of film noir; here it's the aching gleam of '50s small-town purity. You can almost taste the yearning in this snow-crisped Norman Rockwell landscape, untouched by the trials of progress. It's a world that won't grow up.
That's where Polar Express both disturbs and delights: it's smothered by the blanket of one-dimensional Christmas ideals, but does make you feel good. In other words, it reminds you of being a kid, fit to burst with excitement at the possibilities of paper-wrapped goodies, whether they're dropped off by a dubious fat guy in a red suit or parents determined to hold up the masquerade. 'Just believe,' we are implored; follow the party line of easy living and you'll be rewarded with huge presents.
However, you can't help but notice that the message at the soul of the movie is impaired by its own narrative: when you're taken by steam train to meet Santa, it's less a case of having to believe than a getting a heavy dose of irrefutable proof. Then again, was it all just a dream?