ShadowElliot
Banned
Indeed, SA-X is freakier than any other doppelgangers from the Metroid universe. Perhaps because the others were just 'monsters' trying to resemble you, whereas SA-X is a perfect mimic where the player's sense of 'something alien' is conveyed via more roundabout ways - musical themes, the occasional closeup of the pupil-less face seen through the visor, etc.
Man, it gets scary knowing if you screw up, SA-X will attack you on the spot. Plus... those footsteps.