Robert Zemeckis is best known for directing Forrest Gump, Back to the Future, and Castaway. But his real interest was in making movies using famous movie stars as motion-capture actors for CGI puppets. Unfortunately, his ambitions were ahead of the technology of the time, so his efforts like Polar Express, A Christmas Carol, and Beowolf had characters that looked like animated corpses.
Nerdstalgic's video about Zemeckis' uncanny valley oeuvre looks at how the director got "stuck in a digital world that never stuck with audiences."
What Nerdstalgic said about Polar Express:
The key element that Zemeckis overlooked was that the almost real animation style was too close to being lifelike for the general public to accept. If it had been more stylized, it would have been easier to understand and emotionally embraced. However, the film's aesthetic leaves everyone with weird plastic faces, dead eyes, bizarrely fitting clothes, and disturbingly flat mouth movements.