I'm a big fan of the original series because of the far-out concepts every episode. Even today, these shows stand up well because the science aspect is so far on the horizon that none of these concepts have been realized. This episode isn't so heavy on the sci-fi aspect. The writers wonder what if we found a long extinct sea creature that local legend believes is a God.
However, that plot line kind of takes a back seat to a study of characters. We have the wealthy, rugged individualist. We have his companion, a former magazine writer who is in love with him but frustrated that she can't break through to his humanity. We have a scientist who is competent but revealed to be a coward when under stress. And we have a corrupt socialist dictator, who pretends everything is for the people when in fact everything he does is to enhance his own reputation.
I found the ideological struggle between the dictator and the wealthy explorer to be the most fascinating part of the episode. The explorer is a self-made man with little patience for incompetence. The dictator is mostly interested in keeping the reptile for a huge tourist attraction he built that is failing miserably. Since the explorer is a man of few words, his silence at the questions by the dictator speak volumes. You can tell he despises the dictator for robbing his people of their individuality and vainly attempting to deliver them a socialist paradise like some kind of God. As this story comes to a climax some aspect seem kind of rushed. The underwater footage with the reptiles are entertaining. You can tell the producers went all out for these, but of course they can't help but look funny in a Godzilla kind of way. The special effects are exceptional for the early sixties, but they do show their age of course. That's one aspect of the show that makes it even more entertaining.