This is one of the last films on which Willis O'Brien worked. If his name isn't familiar, he's the guy who brought King Kong to life through the miracle of stop-motion cinematography. His work led to the likes of Ray Harryhausen and it's quite enjoyable to watch his creatures come to life. However, I must point out that technically speaking, this is far from O'Brien's best work. In fact, I think the story is far better than the stop-motion special effects.
The story is about a giant marine dinosaur that seems to have been created through the typical menace in 50s films--nuclear radiation. At first, the monster appears in an isolated fishing village and its radioactivity kills or maims. Some (especially Evans) take this very seriously. Everyone does after it attacks London! Will the Brits be okay or are they all destined to be gobbled up like a stack of freshly baked scones?!
This film stars a rather unlikely actor--Gene Evans. Evans was hardly the handsome leading man type and is probably most famous for his gritty sergeant character from Sam Fuller's "Steel Helmet" as well as appearing in Fuller's "Shock Corridor". So, seeing him playing the intellectual scientist was a bit odd but it worked well enough. In fact, the acting all around was very good--no complaints. However, the special effects, at times, looked pretty bad--such as when the creatures is swimming underwater.
By the way, the ending was rather clever. Make sure not to miss it.