With the 50's monster cycle almost over, The Monster that Challenged the World is one of the "lost" entries of the era. While it does fall victim to typical and expected clichés, it also builds some strong character, a rarity for not just the time or the era, but the genre too. It's the best thing going for this low budget piece of filmmaking.
The title may be a little misleading. The monster doesn't really challenge the world so much as it challenges a few local beaches. Still, the body count along with the especially gruesome shots of drained bodies are fairly shocking compared to the tameness of 50's sci-fi.
Lead actor Tim Holt takes charge against the giant "we don't know what it really is but it looks cool on screen" creature. His character doesn't follow the usual stereotypical military director. He's stern, impatient, yet understanding. The loss of life has an effect on him, a surprising move on the part of the writers. Most of these films slap a cigar in the general's mouth and have him spout off lines about nuking the beast. That's, thankfully, not the case here.
That leads me back to the creature. Everything is pulled off practically, which is to be expected. It's well realized, though we're told it's numerous different species, from mollusks to the legendary Kraken. Whatever it is, its bulbous eyes, sharp pinchers, and tiny, eerie legs are fantastically realized. It's not particularly mobile, and the final confrontation is hurt badly as the creature swings around obviously pulled by an off-screen special effects crew. That's one of the few moments when it stands out negatively.
Direction is excellent for the most part. The only missed opportunity is the full reveal of the creature. After a solid 20 minutes of build up and multiple deaths, just inserting footage of the killer on-screen standing alone in the water is disappointing. That's intercut with obvious footage of the lead actors inside a pool during close-ups.