When thinking about the 70's Showa films, if you subtract the obvious - low budget, poor quality etc. What stands out? The cool and strange stories.
Smog Monster, Robots, Cyborgs etc., it was all cool. What was lacking IMO was Godzilla. He didn't match the intensity of his foes. He acted too human, and the suits were too friendly looking. Yes, I know the films were made for a younger crowd, Godzilla was now a Super Hero, but he was too silly.