Robot Monster (1953)

Starring George Nader, Claudia Barrett, Selena Royle, John Mylong, Gregory Moffett
Directed by Phil Tucker
(actor & director credits courtesy IMDB.com)

A young boy imagines a post-apocalyptic future where all of humanity has been wiped from the Earth save for him and his family, who are being stalked by the alien Ro-Man.

Notorious for ending up on several "worst movies of all time" lists, I probably wouldn't put it there, although the film obviously has a number of strikes against it.  Ro-Man and his leader, "The Great Guidance," are costumed in gorilla suits with space helmets on their heads, certainly an odd visual, and the movie's most notable special effects (outside of a bubble machine) are stock footage that's presented multiple times in the movie.  The love scene between Nader and Barrett is rather comical, as is Ro-Man's lust for Barrett, culminating in trying to pull off her dress.  I certainly wouldn't call it boring, the actors are earnest, and the score from future Oscar-winning composer Elmer Bernstein has its charms.  It may not be great cinema, or even good, but it's certainly a memorable piece of work.