This was before I started actually reading science fiction, and my friends and me really liked the science fiction movies that were being shown on the TV when you had about five channels. This movie ranks up there with "The Deadly Mantis" (giant praying mantis), "Them" (the giant ants), and "Tarantula" (the giant tarantula, of course). Being a kid growing up during the height of the space race, science fiction was always an "almost anything goes" genre to occupy a lazy afternoon. This movie is easily competitive with the Japanese monster movies, and I think that the creation of movies like this peaked out at "The Green Slime" (1968).
All you have to do is turn off your brain and throw out your "willing suspension of disbelief." It's just a plain old fun movie, good for everyone to watch on a rainy day. And if it would ever be shown again, I can watch it with popcorn AND a beer.