For a movie from 1981, then "Inseminoid" (aka "Horror Planet") was still entertaining to watch today. After having read reviews that claimed it to be a rip off of "Alien", then I was a bit reluctant to watch it. I will say, however, that while it shares some similarities with "Alien" then it wasn't a rip off.
The story is about a group of interplanar archaeologists who stumble upon a cave-dwelling alien creature. The creature impregnates one of the crew members, and slowly she started to turn into a crazed killer while the alien offspring grows inside her.
Now, the movie is driven by its story and acting talents, and barely relying on the special effects. This wasn't a special effects extravaganza, not by a long shot.
As for the acting, then I will say that people were doing good jobs all round, which was crucial for the movie.
You can't really have an alien creature movie without a proper alien being. The alien in "Inseminoid" actually looked rather interesting and was nicely made. It just wasn't shown as much throughout the entire movie as I would have liked.
All in all, "Inseminoid" is an enjoyable Sci-Fi horror movie. But given its age, it is not a movie that stands out as memorable in comparison to the Sci-Fi horror movies that come out nowadays.