IMDB was being awfully kind by giving Humanoids a 5.5 rating. This film is one big stinking pile of fish poo if you ask me. How bad i s it? Let me count the ways. First of all, it takes itself way too seriously. Director Barbara Peters was one of the few female directors who made trashy exploitation pictures in the 70's and 80's. This kind of film is effective if it tells its story with a wink and a nod. Unfortunately, Humanoids tries to hard to be a genuine horror film. It fails miserably.
Secondly, the creatures in this film look like they were created for a High School play. They have more in common with 1950's B-movie monsters than they do the typical fare found in the 80's. They were meant to evoke terror but are unintentionally funny at best.
Finally, the acting is often stiff and wooden. Some of it has to do with the dialogue. most of it is simply bad acting. There are so many wonderful horror movies that were made in the 1980's, bet scary and trashy ones. I suggest you check them out instead and leave this one rotting away at the bottom of the ocean.
P.S. Roger Corman is uncredited as executive producer of Humanoids. It is hardly his best work and has more in common with the dreadful Monster From the Ocean Floor (1954) than it does The Masque of the Red Death (1964) which is one of his finest efforts.
For more info check out the film's entry in IMDB.