 Producer Richard Gordon later said there were major problems with the film's special effects.He also said that he had a dispute with Anglo-Amalgamated, who did not want the movie to get an X certificate in England, whereas Gordon wanted more horror for the US.Leonard Maltin called it a "blah sci-fi programmer" ; while TV Guide noted, "an intriguing feature in that it was among the first to examine the possibilities of psychological manipulation and brainwashing."