Gort is an old favorite of mine, because he wasn't cute, he wasn't trying to please, and he wasn't simply another anthropomorphized machine. He had no lines at all in The Day the Earth Stood Still. And yet he did have a personality, an all-business one, and he was willing to stay the law long enough to revive Klaatu and take a stab at saving the Earth instead of pulverizing it. That showed more the compassion of his creators than anything that might have been present within the machine itself, and yet what is a machine, but an appendage of ourselves?
He projected the sheer menace of an intelligent machine, and seemed to have few of the safeguards built in that Asimov placed in his robots. For that, his creep factor was extremely high. And as a guest character for Halloween, he works cheap, too!