"Leonard Maltin awarded the film three out of four stars, writing: "Archetypal '50s monster movie has been copied so often that some of the edge is gone, but ... is still entertaining, with juicy atmosphere and luminous underwater photography sequences".
Since its original release, Them! has become generally regarded as one of the best science fiction films of the 1950s. Bill Warren described it as " ... tight, fast-paced and credible. The picture is suspenseful". The Aurum Film Encyclopedia: Science Fiction noted, "Them! is one of the best American science fiction films of the fifties".
New York Times noted that George Pal had followed up on his other prophetic epic, Destination Moon: "... this time the science soothsayer, whose forecasts have the virtue, at least, of being represented in provocative visual terms, offers rather cold comfort for those scholars who would string along with him. One of the worlds which he arranged to have collide is ours".
"A first rate science-fiction-horror melodrama", declared Harrison's Reports, adding, "the action grips one's attention from the opening to the closing scenes, and is filled with suspenseful, spine-chilling situations that will keep movie-goers on the edge of their seats."
Los Angeles Times called the film "a fascinating exercise in imagination, as terrifying as it is funny. Science-fiction admirers who are accustomed to finding food for thought as well as vicarious thrills in such flights of fancy will not be disappointed, either."
The film is now considered to be one of the best films of 1951 and one of the great science fiction films of the 1950s. Time magazine named The Thing from Another World "the greatest 1950s sci-fi movie".
War of the Worlds was presented with a Hugo Award in the category of Best Dramatic Presentation. The Martians were ranked the 27th best villains in the American Film Institute's list AFI's 100 Years...100 Heroes and Villains.
Los Angeles Times wrote that the film was "more than another science-fiction movie, with the emphasis on fiction; it is a genuinely thought-through concept of the future, and the production MGM has bestowed on it gives new breadth and dimension to that time-worn phrase, 'out of this world.' "
The Day the Earth Stood Still (TDTESS) was ranked number 82 on American Film Institute's 100 Years ... 100 Thrills, a list of America's most heart-pounding films. It placed number 67 on a similar list 100 Years ... 100 Cheers, a list of America's most inspiring films.
The film was acknowledged as the 5th-best film in the science-fiction genre of American Film Institute's "Top Ten Classic" American film genres. TDTESS was selected by The New York Times as one of The Best 1000 Movies Ever Made.
Invasion of the Body Snatchers was acknowledged as the 9th-best film in the science-fiction genre of American Film Institute's "Top Ten Classic" American film genres. The film was also placed on AFI's 100 Years ... 100 Thrills, a list of America's most heart-pounding films.
The film was included on Bravo's 100 Scariest Movie Moments. IGN ranked it as the 15th-best sci-fi picture. Time magazine included Invasion of the Body Snatchers on their list of 100 all-time best films, the top 10 1950s Sci-Fi Movies, and Top 25 Horror Films.
Entertainment Weekly listed it as the 53rd best movie of all time. The book Four Star Movies: The 101 Greatest Films of All Time placed the movie at #60.
