Released a year earlier this has a very similar plot to, and was an influence on, Godzilla; atomic testing unleashes the titular beast who then wreaks havoc on the nearest metropolis.
This has a promising start, jumping straight into the story and using a narrator to bypass the need to explain the situation via dialogue or develop any characters. The beast appears but then the film slumps for quite a while as a survivor tries to research and track the creature in order to warn the world. There's also time for a lacklustre romance before we finally get an extended fight with the beast.
The finale is okay, and fairly unusual, but since the film drags whenever Ray Harryhausen's dinosaur is not on screen I had mostly lost interest by that point. 5/10.