The villains of this film are beings from the underwater kingdom of Seatopia, frustrated with humans' nuclear-bomb testings, which ravaged their kingdom. Therefore, they sent their monster god Megalon, an over-sized cockroach, to destroy mankind (pretty sensitive, couldn't they just reach out to the humans and let them know they live downstairs, so therefore, quit with the bomb testings?).
Toho utilized the overused alien-invasion plot again, making this film the a rush-through production job. Tons of stock footage were used and the plot was very plain. This film is basically an "aliens and monsters invade Earth, and Godzilla and a robot arrives and defeats them and saves Earth story." There are no subplots, significance, irony and female leads. What made up for this movie, though, is the monster wrestling-like battle at the climax. After getting pretty beaten up by Gigan at the previous fight in "Godzilla vs. Gigan," Godzilla this time really gave Gigan a taste of his own medicine. Even giant-beetle Megalon couldn't hold up a strong battle against Godzilla. Jet Jaquer was Godzilla's partner-in-crime, a giant robot made to capitalize on the Ultraman and Zone Fighter trilogies that were popular in Japan by the time this movie came out, so I guess Godzilla deserves the right to have a robot as his sidekick at least once. Unfortuntately, Jet Jaguar wasn't emphasized enough. There should have been more scenes depicting him as a "superhero" (like saving a life or stopping a robbery like most superheros do). It still bothers me why the Seatopians need to steal Jet-Jaguar and use it to guide Megalon to Tokyo. In previous Godzilla movies, monsters just find their way to the city and start trampling. Why the heck does Megalon need a tour guide?
To sum it all, a rushed film with lots of stock footage and sub-par characters. But, an exciting monster battle at the end.
Grade C