Roger Ebert was completely floored by how good it was:
The Polar Express is a movie for more than one season; it will become a perennial, shared by the generations. It has a haunting, magical quality because it has imagined its world freshly and played true to it, sidestepping all the tiresome Christmas cliches that children have inflicted on them this time of year.
I haven't been as certain a film would become a Christmas classic since Ralphie shot his eye out with the Official Red Ryder Carbine-Action Two-Hundred-Shot Range Model in A Christmas Story.
Kids always talk during children's movies, but I can't recall one in which every single child in the theater talked out loud to the screen, urging the characters in suspensful moments.
At one point near the end, I glanced back at the projector. Four or five children were standing up in the row behind me, inches from my face, and their hands were clasped to the seats as they watched in absolute awe.
My daughter was one of those children at our community theater.
Merry Christmas :)