This is one of those horror classics which has aged pretty poorly, with both the script and the effects having dated kind of horribly. But the production values outside of the effects are otherwise excellent and it really is on the good side of horror films of the period.
I saw the remake when it came out but I had never seen the original. I didn’t actually realize it was a British movie! Once I got over that I noticed it’s a very peculiar kind of science fiction horror film, in that the victims are basically aware of the threat from the very beginning of the film. It’s a strange approach that makes it rather unique in the annals of horror movies, where usually disbelief plays a very important role.
The script has dated rather horribly – there are leaps and logic but, worse, there is just so much that is incorrect, both scientifically and socially. As to the latter, I would suggest anyone who doubts systemic sexism to watch this movie and listen to the way Zellaby talks to his wife. (By the way, those actors are 26 years apart. Ewww.) And there is a lot of scientific mumbojumbo that peppers the script.
And the effects have also horribly dated, including the use of stills and models for the biggest effects. (It’s kind of crazy to think that such an otherwise mainstream film used still photography and thought it could get away with it as late as 1960.) They are basically laughable at this remove, though I don’t know how much 1960 audiences would have noticed.
But it’s otherwise very well made. The cast is pretty good, it’s well shot and the pacing is brisk, to put it mildly. So even though the film has dated pretty horribly when it comes to effects and dialogue, it’s still one of the better horror films of its day. And, frankly, I can’t think of too many other British horror films of this era.