Arc Fatigue: To its limited credit, the movie cut out the chapters involving the gold mining and the long search for radiation.
Critical Dissonance: It overcame mixed-to-negative reviews to reach the top of The New York Times' bestseller list, though bulk-buying by Scientologists was alleged to have played a part. The movie averted this by losing money and being hated by a massive majority of critics and the public alike.
Ending Fatigue: The book's climax is around page 320, and there's an obvious enough ending when the humans have retaken their planet. And then the book keeps going for 700 more pages.
Inferred Holocaust: Some of the Psychlo bases on other worlds were in the middle of occupied cities. When Jonnie checks on them a year or so after his attack on the Psychlo Empire, he finds blasted, lifeless ruins, but thinks no more of it.
Squick: The Bittie and Pattie relationship. If we're optimistic and they're both about the same age, we have two eight-year-olds who decide to get married someday. Then Bittie dies, and Pattie goes into a deep depression. And then years pass and Pattie still hasn't moved on, goes to Bittie's tomb, and demands that a parson marry them.
Unfortunate Implications: Hubbard named one alien race "Chinko" after the anti-Chinese slur 'chink.' (The movie changed it to "Clinko" but didn't make it much better, with the Clinko hologram instructor speaking with a thick accent and being stereotypically servile.)
Adaptation Displacement: And to most viewers, for the worse. While the book was a bestseller in its day, it sold to a very niche audience. The film was intended to be a mass audiencepleasing blockbuster, and it is safe to say it failed to achieve that goal.
Alternative Character Interpretation: The Psychlos are so stupid and childish, it seems impossible they could have ever built their civilisation without destroying themselves with their petty infighting. It actually makes a lot more sense if one imagines that Psychlos were themselves a race of backward slaves whose masters invaded Earth a millennium before, but died out mysteriously during the interim, leaving behind all their technology for the Psychlos to abuse.
SF Debris commented that their use of gas-drones explains their military superiority: they can move in and destroy the local population without having a Psychlo brain screwing it up.
Awesome Music: Elia Cmíral's score is one of the few good things about the movie. A couple of examples: the aptly named "Battlefield Earth Theme", which plays over the opening zoom-in to Earth and pan through the Rocky Mountains, and "The Dome", which underscores Jonnie's trip to the human processing center, shooting of the wrangler, and our introduction to Terl.
Big-Lipped Alligator Moment: The "plot" is so nonsensical and poorly constructed that very few of the Psychlos' scenes seem to flow logically into one another, but the hysterically "dramatic" water hose scene, where a few bored-looking Psychlos spray water on human cavemen, who thrash around like they're being sprayed with acid and slap ineffectually at the Psychlos, is bad even for this plot. This goes on for about a minute, and then the movie just kind of awkwardly moves on like it's embarrassed by what it just showed to the audience. Several critics speculated that the scene was probably intended as a Shout-Out to the Its a madhouse! scene from Planet of the Apes (1968), but the way its shot ends up causing the homage to be completely lost.
Bile Fascination: The movie regularly places in the top (bottom?) ten of many "worst movies of all time" lists made by critics and casual viewers alike.
Travolta's "While you were still learning to spell your name!" line is funny if you look at his pronunciation of IdinaMenzel.
One of Terl's lines in the infamous cow scene is "I graduated top marksman in my class and I can kill any one of you at over a thousand paces", which is nearly a verbatim quotation of a line from the memetic Navy Seal Copypasta.
Ho Yay: One of Jonnie's followers spends much of the movie looking soulfully at his leader. Jonnie even cuts off a lock of his hair for him, and he wraps it around his fist as a sort of talisman. Arguably, Jonnie has more chemistry with this guy than with his designated love interest.
The RiffTrax guys had no trouble picking up on this subtext. Whenever the guy makes puppy dog eyes at Jonnie, they start tearfully muttering "Love you!"
Idiot Plot: Characters aren't making the wisest decisions in this film. Jonnie's plan would have never worked under a competent boss who would realize things like that he and his people claimed to have 'mined' bricks of smelted gold. Thankfully, Terl is a moron and never evinces any suspicions of the humans. In fact, his myopic greed is what kicks off this idiot plot in the first place.
Further compounding this is the astonishing stupidity of the entire Psychlo race, who seem in full denial of the evident intelligence of the human race and after nearly a millennium of occupation still lack even basic understanding of how human civilization once thrived. It comes back to bite them in their collective rears hard when Terl's plans go awry.
It also relies on the facts that after a millennium of occupation, the Psychlos never managed to locate facilties housing gold and military equipment. The 'primitive' rebels discovered them seemingly without breaking a sweat.
The entire film seems bent on making the viewers as queasy and uncomfortable as possible. From the dirty, grimy actors and environments, to the physically repulsive Psychlos (of both sexes) and ridiculous costume design. Not to mention the overly-harsh filters, making everything too blue, or too green, or whatever. This may have been the point, but that's little consolation.
Overshadowed by Controversy: Before its release, studios thought this was a risky investment despite Travolta's commitment to it. Studios expected it would require a prohibitively large effects budget, thought the story was outdated, and feared negative publicity due to Travolta's involvement with Scientology. Since its release, it's become more notorious as a criticallynukedBox Office Bomb.
Snark Bait: Roger Ebert wasn't kidding when he said this would be the punchline for jokes about bad movies for decades to come.
So Bad, It's Good: A lot of people called it the greatest unintentionally hilarious sci-fi movie ever made. If you can get past the Nausea Fuel, it can almost pass for a incredible comedy.
Special Effect Failure: The movie has a few cases of this. One of the most infamous examples is when Terl demonstrates his weapon to his human workers by shooting the leg off a cow. It's clear that when Terl does this it's just a leg being pulled off a model cow by a concealed string.
The laser gun effects demonstrated during the Psychlos' first appearance would barely be passable in a laser tag game.
They Wasted a Perfectly Good Character: Zete is the highest-ranked Psychlo character in the film, connected to both a "home office" which runs the Psychlo empire as a corporation and at least one (unseen) senator who represents the empire's politicians. He gets one scene and all he does is notify Terl that his assignment on Earth has been extended.
Visual Effects of Awesome: While the CGI is generally mediocre at best, the collapse of the Psychlo dome and the resulting destruction of much of Denver (which, unlike most of the film's other effects, was achieved with physical models) is surprisingly great.
The entire Psychlo race counts as this, having enslaved the Earth for a millennium and still having zero understanding of the human race whatsoever. They even contemplated the possibility that dogs were superior to humans, and even attempted to exploit them as slave labor.
Their most egregious lapse in intelligence, however, has to be how in nearly a thousand years of mining for gold, they somehow never found Fort Knox. This one doesn't even have the excuse of being from the book.
Chris Stuckmann points out a scene where Terl gives Jonnie a gun for some reason. Chris points out that Jonnie could of just shot Terl right than and there. Instead, he just kinda stares at Terl, and then shoots some random goon. Ironically, this actually ends up benefiting Jonnie in the longer run, as had he killed Terl then his job would likely have been taken over by Ker, who lacks the same lethal combination of ambition and stupidity that Terl has, and thus would never have put Jonnie in a position to be able to overthrow the Psychlos.
Chris Stuckmann also points out that Terl gives Jonnie a knowledge boost about everything, including how to defeat Terl.
WTH, Costuming Department?: The Psychlos themselves, prominently featuring large elongated heads and dreadlocks, with enhanced codpieces and claws among other things. And that says nothing of those ridiculous jumpsuits...
The Psychlos' means of breathing in Earth's oxygen-rich atmosphere? Sticking rubber hoses up their noses.
The Planetship, with his exaggerated chin, also stands out as such.