Technology aside, the real question is whether or not the movie works. Its source material, after all, is a children's storybook less than 30 pages long, in which a boy takes a magic train ride on Christmas Eve to meet Santa Claus at the North Pole. At least you don't have to worry about spoilers in any reviews -- it's not like they're going to change the story so that he doesn't meet Santa. As it turns out, the book is used as a source for the very beginning of the movie, and for the final twenty minutes. In between, director Robert Zemeckis has created an action movie for kids. Using the simple-enough setting of a moving train, Polar Express is perhaps the most literal roller-coaster ride of a movie since the climax of Indiana Jones and the Temple of Doom.
Our hero, known only as "Hero Boy" (voiced by Spy Kids' Daryl Sabara, facial acting by Hanks, additional physical movement by Josh Hutcherson), is the classic kid who's on the verge of disbelieving Santa stories. In fact, he's even put together a file of evidence against the existence of the Fat One, including a photo of one store Santa with a fake beard and several others on strike. Later, he will see a mechanical Santa in a store window that seems to bear out his suspicion.
So when a large train emerges from the mist like in one of those THX sound trailers, offering him a ride to the North Pole, he's a bit skeptical, but decides to climb aboard at the last minute, whereupon he meets Hero Girl (voice and face-acting by The Matrix Revolutions' Nona Gaye, additional physical performance by Chantel Valdivieso, singing voice by Meagan Moore) and Know-It-All Boy (voice and face by Eddie Deezen, additional movement by Jimmy "Jax" Pinchak), who assure him that indeed, they are going to see Santa Claus.
The source of much of the ensuing drama is the token poor kid, who also happens to be the only one with a name: Billy. In a major casting coup, Billy's face-acting is done by Hanks' former Bosom Buddies co-star Peter Scolari, with voice by Jimmy Bennett, singing voice by Matthew Hall, and additional movement by Hayden McFarland, though the CG character is a dead ringer for Haley Joel Osment. Got all that? Okay. Billy, being a loner, sits in a separate carriage, so that any other kid who wishes to talk to him or share a cup of hot chocolate must walk across a train coupling that's wide open and exposed to all the elements. There's plenty of opportunity to fall off making the jump, and even more so once the characters start walking along the roof of the train (we'd tell you why they do that, but might as well leave some surprises).
So given the complex acting credits in this thing, you're probably wondering how well the characters come across. First, note that unlike, say, Final Fantasy, these are stylized people who aren't intended to be 100 percent photo-real. That said, the detail is amazing, even down to the hint of moistness in the eyes. The kids are extremely well done, and even those who think they look artificial at first glance will likely warm to their performances. Same goes for Hanks' conductor, but not, alas, for his Santa, who looks like porcelain and sounds like Hanks doing a bad Ian McKellen impersonation. Hanks also plays a mysterious hobo who may be either angel or ghost (bets are presumably hedged so as not to offend fundamentalist Christians, who find all ghost stories occultist), and that character is a bit plastic-looking. Santa's elves come off the worst -- hideous things that look half-done, and one of them who's modeled on Aerosmith's Steven Tyler is doubly ugly. One other minor CG nitpick -- none of the falling snowflakes ever lands on anyone who's standing outside.
Zemeckis' runaway-train action stuff is fantastic, though it may induce vertigo in older viewers while pleasing teenage boys who won't admit to liking the flick (this may be the darkest G-rated film ever made). Where the movie falters is when it gets back to the book and delivers time-honored platitudes about how the spirit of Christmas is in every one of us, and Santa is the symbol of the spirit of giving, etc., etc. Young children may never have heard this stuff before, but you have, many times.
That said, if you have a chance to see the 3-D IMAX version of the movie, ignore any objections. Viewed on a grand scale and coming out of the screen, The Polar Express is a groundbreaking spectacle that makes you feel like you're at the beginning of something, like the first color film or the original Cinerama epics, and writ large, you'll appreciate the subtleties of "performance capture" even more. When the climax turns to sap, it is nonetheless soooo cool to look at that you won't care. But if your only choice is a regular 2-D screen, The Polar Express is still three-fourths of a great movie.