I don't know whether it's the vaguely-organic yet malformed-looking legs like something from Silent Hill, the incessant buzzing, or some combination of all these and more but there's something inherently nasty about this robot.
Also, this bastard packs a double-whammy of being skin-crawlingly creepy and invincible, or at least impossible to knock down.
Just imagine this monstrosity coming at you across a post-apocalyptic landscape, covered in blood, packing a Gatling gun turret and making that awful buzzing noise like a giant mosquito from hell.

Boston Dynamics just released a new video of the Big Dog on ice and snow, and also demoing its walking gait.