this was one of those $.50 cent deals of yore---and far more complex than most realize---and it was in color! not only are the effects extraordinary, vs. crap like 'earth vs. the flying saucers'---the real 'killer' is the 'universality of plot'---everything hinges on two principles---the ancient concept of a hidden incestuous-thinking father's desire for his daughter, and the idea of what would happen should a world's tech reach the point where all citizen's desires become manifest.
needless to say if everyone we wished dead gets dead, not many, if any left---and that became the fate of the 'forbidden' planet's populace---rather modern, actually. unfortunately the 'gear' of 'The Krell'---wasted by ignorance, remains, and 'Morpheus', the incestuous father, knows how to access such tech---and does so, to prevent losing his daughter to another. ancient plot, beautifully rendered.
and considering its age, it remains a stunning suspense, action, human-emotion classic---and visually very modern---don't pass this one up---it presages all modern sci-fi---and its pscychological content elevates it, beyond any genre---a timeless work---
and the soundtract! you will see/hear no pure 'synth' and perfectly syched Moog background---a 'not miss'---