Toho's bid to merge the Godzilla series with their popular alien-invasion films resulted in this entertainingly goofy entry. The plot involves the discovery of the mysterious Planet X in our solar system, leading to a joint U.S./Japanese space exploratory mission. The explorers bump into some aliens with no fashion sense whatsoever (even for 1965), who claim their planet has been under constant attack from the powerful Monster Zero -- also known to Godzilla fans as Ghidrah, the three-headed monster from the previous year. The aliens suggest a deal with the Earthlings: if they can "borrow" Godzilla and Rodan to help rid their planet of Ghidrah, they will cure all of humankind's diseases in return. Of course, this is actually an elaborate ruse to rid the Earth of its monstrous defenders, leaving it vulnerable to invasion. As always, it's up to a handful of resourceful characters -- including token American Nick Adams and series regular Akira Takarada -- to save the day and return Earth's monsters for the requisite city-smashing finale. After a slow start, this movie serves up a good portion of flashy pyrotechnics and noisy monster-grappling but lapses into several moments of deliberate silliness (particularly Godzilla's goofy Irish jig) and rampant use of ill-fitting footage from previous monster installments.
~ Cavett Binion, All Movie Guide