Well I can tell you this scared the bejeesus out of me when I was kid.
Watching it today, there are three things of note.
The first is the military footage. The virtual budget of this was millions of dollars because of the military supplied footage. It was defense policy to let the Soviets know of our massive three-tiered air defense and there was an office to so publicize. The idea was to convince the Russians that an attack couldn't possibly work, that the thing really existed. That's why the Pentagon subsidized these things. The scripts were therefore friendly to military success at the end, too.
A solid third of this is from the department of defense, no model planes here.
Perry Mason, the detecting lawyer was a literary phenomenon when this was made, the books about him being outsold only by the Bible. And there was a very popular TeeVee show based on him. Perry's own detective was a guy played by the detective here. And his sidekick is a Della Street (the third member of the gang) lookalike. It was like having Indiana Jones appear. The effect is lost today but was quite something in the day.
The third remarkable thing is what scares us. What we fear in our imagination is largely defined by movies. And what movies use to frighten us is tightly constrained by what they can show. In the fifties, that was often disappearing or morphing things, guys in rubber suits and small things made big by trick photography. "Them" was probably the first giant bug movie, but it used real bugs. This is already a second generation, using stop motion.
The footage of Aleutians borrowed from an older film is great, really great.
Ted's Evaluation -- 2 of 3: Has some interesting elements.