This has some of the highest production values, some of the best FX sequences, the best musical scoring and some of the best acting to be seen in any Kaiju film. Personally, I rate this as 3rd or 4th all-time best in the Kaiju genre, behind such uber-classics as Godzilla, Invasion of the Astro-Monster, and War of the Gargantuas.
Ishiro Honda was the greatest auteur of Kaiju. He was not only the D.W. Griffith of that genre, he was also the Orson Welles. His Kaiju films can be put into 3 rough categories: earnest (i.e. Godzilla, War of the Gargantuas); surreal (Mushroom People); and camp (Invasion of the Astro Monster).
This film is mostly in the earnest category, but the sequence with the long tailed mechanical monster hints at Honda’s immanent surreal and camp tendencies.
Anyhow, this is definitely a very well-made Kaiju, but it is a little slow in some places and the whole strategy of the Mysterians for conquering Earth has some serious flaws. Nonetheless, the idea of alien invaders occupying Japanese territory and and seeking total domination, not to mention the aliens’ designs on the local women, is interesting. And surely this storyline must reflect Honda’s attitudes toward the American occupation forces which still were maintaining high visibility in Japan in this period.
It is my understanding that this film was originally released in Cinemascope or the equivalent, and it really would have been a gas to see it on the big screen that way. The battles between the Earth forces in their strange slow-moving aerial battleships and the Mysterians’ ray weapons, in glorious color and with the orchestra playing in full stereo, must have been a kick.
Of less interest is the fact that the aliens in this film seem to be the direct inspiration for a dreadful yet popular 1990’s children’s TV show, the Mighty Morphin Power Rangers.