With the exception of Tarantula, which is more of a giant insect amok film than it is a mad scientist film, all of these 1950s mad scientist entries are backward looking. They can be seen as better budgeted versions of PRC/Monogram mad scientist films and even seek to sell themselves by association with those who were star players of the genre in the previous decade, featuring familiar names like Bela Lugosi, Basil Rathbone and here John Carradine. As the same time, the mad scientist genre was clearly recognising that it was a dying breed the title The Unearthly gives the impression that this is a mad scientist film that is trying to sell itself by an appeal to the new science-fiction and alien invaders fad.
The Unearthly hums along passably as a B movie. It looks somewhat better than most of the entries put out during the 1940s, although is still not that well budgeted. John Carradines scientist lacks much in the way of a laboratory. The other complaint might be that almost the entire film takes inside the single locale of an ordinary house and ventures outside only on about two occasions. The exact nature of the experiments that John Carradine are conducting is somewhat vague and so the film never derives much horror from this or what he is threatening to do. As a result, most of the film is concentrated around the playing off of the tensions between the characters, at which the film often feels more like one of the B crime dramas of the era escaped convict on the run hiding out in the house, the sympathetic girl he develops an interest in, he trying to find the doctors secrets and so on. As a mad scientist film, it stirs the assemblage of cliches but never lets the pot boil much until the climax.
What must be said is that next to The Black Sleep, The Unearthly is a mad scientist film that features one of the best cast of regulars from these movies brought together under one roof. There is John Carradine, a Dracula in two of the Universal sequels, who made a veritable career out of parts like this for about five decades. Here Carradine is in his prime and on fine form as the ruthlessly blackmailing mad scientist. There is Allison Hayes who had a minor B-movie career during the 1950s in parts such as The Disembodied (1957), The Undead (1957), Zombies of Mora Tau (1957), The Hypnotic Eye (1960) and especially gaining a cult fame as the title figure in Attack of the 50 Foot Woman (1958). There is also wrestler Tor Johnson, an Edward D. Wood Jr regular in Bride of the Monster, Plan 9 from Outer Space (1959) and Night of the Ghouls (1960) and other films like The Black Sleep and The Beast of Yucca Flats (1961) as the hulking manservant here he even plays the character of Lobo that he did in Bride of the Monster.
Director Brooke L. Peters was in fact a Russian emigre Boris Petroff who made a handful of crime thrillers of the decade with Outcasts of the City (1958), Anatomy of a Psycho (1961), which is not a genre film despite its title, and Shotgun Wedding (1963). Peters/Petroffs one other genre entry was as producer/writer of the prehistoric lost world film Two Lost Worlds (1950).