Sci-Fi/Horror is a sub-genre of horror that some people have a problem with. Sci-Fi fans have a tendency to hate the merging with horror.
Planet of the Vampires: Mario Bava’s creepy 60s minor classic holds up really well. Two spaceships respond to a distress call on an alien planet and discover a race of monsters who possess the crews.
Alien: Ridley Scott’s masterpiece. If you have not seen this film do so now. A highly effective movie that has a lot in common with Planet of the Vampires (not sure if the filmmakers had seen that film or not) and uses elements from the writings of H.P. Lovecraft.
Lifeforce: Tobe Hooper (director The Texas Chainsaw Massacre) and Dan O’Bannon (writer Alien) made a film that goes beyond expectations. An astronaut returns to Earth after his crew discover an alien spacecraft hidden within a comet and awakening three aliens. The aliens arrive on Earth and soon the apocalypse is under way. The main alien is a beautiful woman who wanders around naked the majority of the time she’s onscreen. It’s impossible to take this film seriously, but it remains highly entertaining.
John Carpenter’s The Thing: This film has aged really well. When it was first released it didn’t do well at the box office. The main reason why was ET came out around the same time. Amazing monster EFX and a story that will creep you out.
Event Horizon: A flawed, but very effective film. This movie has some unique visuals that must be seen to be believed.
Species: This film is very entertaining. SETI makes the mistake of creating a human/alien hybrid using a dna sequence they receive from an alien race. The hybrid turns out to be a monster looking to mate. The fact it’s a beautiful woman who has a tendency to take off her clothing at the drop of a hat helps.