When I first saw this episode back in 1968, I felt fear--it looked exactly the way I always pictured hell.
Now it looks cheesy, of course, but I was watching some eps from STAR TREK's first season, and those FX looked equally terrible. Can't compare 35+ years ago with today. But great special effects don't make up for poor storytelling, and DS told some of the most fascinating stories ever! It lingers in the mind, all these years later.
Love, Robinr