Film Rotation pointed me toward an article that does an excellent job of explaining and demonstrating how motion-capture technology itself (as used in computer-animated movies) is only the means to an end, not the end itself. In the case of The Polar Express, the author argues (and shows), the animators botched the detail work, resulting in bizarre-looking, seemingly possessed characters. By way of comparison, he offers Gollum and the decidedly unrealistic CGI of The Incredibles.