The reviews of the original film aren't especially positive, but it did better than expected and spawned a number of sequels. It's got a lot of spoken infodump material, where some scientist explains all about this new method guaranteed to destroy the monster interspersed with segments showing that method failing. There is a subplot involving an adorable child who loves turtles, but those scenes are few.
In 1966 it was re-edited for an American audience as Gammera the Invincible:
with Brian Donlevy in new scenes. This one is dubbed in English.