It would be cruel to force anyone to make such a distinction, but if you HAD to compile a list of the worst movies John Travolta has ever been in, "Battlefield Earth" would definitely be in the top 50. Is it worse than "Old Dogs," "Swordfish," "Be Cool," "Wild Hogs," "Staying Alive," "Two of a Kind," "Look Who's Talking Now," "White Man's Burden," "Michael," "The General's Daughter," "Lucky Numbers," "Basic," "The Punisher," or "Domestic Disturbance"? Only the highly calibrated instruments of trained scientists could say for sure.
But "Battlefield Earth" is definitely the worst Travolta film to be based on a Scientology novel (just edging out "Urban Cowboy"). It was a passion project for the actor, whose devotion to Scientology is matched only by his devotion to pie, and he used all the fame and influence he'd accumulated after "Pulp Fiction" to get the film made. Which means the person who's actually responsible for "Battlefield Earth" is Quentin Tarantino, aka the devil.
"BFE" (as the kids call it) is set in the year 3000, when man is an endangered species and Earth is ruled by a villainous race of Klingon-like aliens called Psychlos. (L. Ron Hubbard took George Lucas' workshop on subtle character naming.) The Psychlos are mean, arrogant, technologically advanced, and disgusted by primitive humans, who are all either enslaved by the aliens to mine the Earth's resources, or live in dismal camps in the wilderness (like Burning Man, only more civilized). The Psychlos are also taller than humans, a visual effect that is achieved through the clever cinematic technique of almost never putting Psychlos and humans in the same shot.
Now, the Psychlos don't intend to stay here forever. They're only on Earth to dig up our natural resources and take them back to their home planet. You have to admit this is fair, as we would definitely do the same to them if we could. Travolta plays the Psychlo security chief currently in charge around here, an especially fey and frequently cackling bully by the name of Terl. He's assisted by a stooge/whipping boy named Ker (Forest Whitaker), who accepts Terl's abuse and offers loyalty in return, in the manner of Lex Luthor and Otis, or Dr. Forrester and TV's Frank, or Adam Sandler and moviegoers. Terl hates "man-animals," as they're known, hates Earth, hates his Psychlo bosses who gave him this assignment, hates his friends, hates everyone. He hates speaking in a normal tone of voice, hates nuance, hates layered performances, hates being taken seriously as a villain, hates starring in movies that are praiseworthy, hates not being a laughingstock.
Meanwhile, living like savages for hundreds of years has made humans kind of stupid. They're illiterate, superstitious, and don't believe in science. There are probably some ways that they're different from modern humans, too. But one of them, a strong-willed warrior named Jonnie (Barry Pepper), refuses to accept his fate. Bravely embarking on a bold journey to change his people's destiny, he ventures into a Psychlo outpost and is immediately captured and enslaved. Ah, but he is to become their Spartacus! He gets hold of a Psychlo guard's gun during a scuffle and fires it before being recaptured. Terl is amazed that a human was capable of shooting a gun at all, which shows how much he knows about humans.
Recognizing that this particular man-animal might be smarter than the average man-animal, Terl hatches a plan. He'll use a "knowledge machine" (probably a Scientology thing?) to teach Jonnie some basic skills, then make him lead a group of other man-animals on a gold-mining expedition, all without the knowledge of Terl's bosses. Terl will keep the gold for himself and use it to live like a king when he gets back to his home planet. (Why would gold be valuable anywhere other than Earth?) (SHH!) It is a foolproof plan, except for the part where Terl puts Jonnie in the knowledge machine and Jonnie learns not just gold-mining skills but also the Psychlos' history, language, and weaknesses, which he uses against them when he leads the human uprising. Terl should have learned the lesson of every scientist in every movie about animal attacks: it never turns out to have been a good idea to make the animals smarter.
That's especially true when the scientists aren't too bright themselves. Wanting to know how to motivate the man-animals to work, Terl sets out to learn what kind of food they like. He does this by letting Jonnie and several others think they have escaped into the mountains, then following them to see what they eat when left to their own devices -- a needlessly elaborate method of obtaining an answer that could also be obtained by just asking them. (By the way, if you try this with me, I will lead you to a Wendy's.) And then, because there's no real food out there in the mountains and the man-animals are starving, they eat some rats, which leads Terl to conclude that their favorite food is rat. How embarrassing it must have been for mankind to be vanquished by a race that doesn't even understand the scientific method! On the other hand, maybe Terl is exceptionally stupid and it's racist of me to judge all Psychlos by his example. But on a third hand, they've been on Earth for a thousand years and didn't know we had gold.
Under Jonnie's direction, the humans have a plan of their own. They pretend to mine gold while actually getting it from Fort Knox, which is 1) nearby, 2) intact, and 3) accessible. With all the time they save, they can plan their revolt, which also involves going to Fort Hood, Texas, and learning to fly the Army's planes, which are 1) in working condition, 2) fueled up, and 3) evidently quite easy to learn to fly, because a group of humans who haven't seen technology in ten centuries pick it up in a week. The Psychlos are ultimately defeated, astonished that they could be conquered by a species as primitive as humans. "Primitive" may sound like an unfair assessment, but keep in mind, it was humans who made "Battlefield Earth."