They used to be much more subtle about such things. Any George Lucas movie (for example) inspires dozens of knockoffs, and while, say, King Solomon's Mines doesn't begin to approach the appeal of Indiana Jones and the Temple of Doom, it at least has its own merits to commend it.
You can see the influence of Ridley Scott's Alien on Roger Corman's Galaxy of Terror. The former is a much better movie, but the latter makes no attempt to fool anybody. It's as if Corman is saying, "look, Galaxy is no Alien, but I can give you ten of these while you're waiting for the next one of those, and hey, I got James Cameron doin' production design on this one, so there's that."
Galaxy of Terror concerns the planet Morganthus, where a spaceship has crashed and left no survivors. The Planet Master has sent the starship Quest to Morganthus on a salvage mission. captain Trantor (Grace Zabriskie), the commander of the mission, is the lone survivor of a famous (but never explained) disaster which has left her with PTSD. Trantor is the kind of erratic mess that would never be hand-picked to command a mission in real life: the moment all the crew are aboard, she announces that they will launch in 30 seconds, followed by a dangerous hyperspace jump. Everyone scrambles to get into appropriate safety positions, and many pieces of mind are set aside so that they may be given to Trantor when it's safe to stomp around and gesticulate wildly again. The Quest has a crash-landing on Morganthus. Everybody survives, but Captain Trantor is probably regretting her showy behavior.
The crew decide to begin exploring Morganthus, and this being a sci-fi/horror film, that exploration does not go well. There are booby traps, tentacles, and centipedes, and eventually they figure out that the planet is confronting each crewmember with his or her worst fears.
So, we've got shades of Alien and Forbidden Planet, with a little of Star Wars/Trek mixed in with whatever other sci-fi tropes were in the public consciousness in 1981. As usual, I'm withholding a lot of information, and there's an explanation behind all of this. There's also a shadowy conspiracy, an infamous "tentacle rape" scene which is more embarrassing than anything else, and a lot of portentous dialogue that doesn't go anywhere. This is the kind of movie where characters are constantly dropping vague references to events outside of the movie's timeline. The purpose is to inflate the scope of the movie, and make it feel like an epic, but it just feels overwrought.
Which is not to say that it's a waste of time. It's fun, in a low-budget-version-of-Event Horizon sort of way. If nothing else, the cast is pretty incredible: Sid Haig shows up and lumbers around as the Quest's resident Big Lug, and Zalman King gets to chew a lot of scenery. Robert Englund doesn't, but this was still pretty early in his career. Ray Walston makes a good
Grace Zabriskie: has she ever played a character who wasn't under considerable stress? I can't think of one, but she must have. Her face is good at looking perpetually horrified, just on the brink of mental collapse.
Here's the trailer.