These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Arc Fatigue: The movie wisely cut out the chapters involving the mining of the gold, or the long search for radiation.
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.
Marty Stu: Jonnie is physically perfect despite hailing from a village plagued by radiation, an awesome fighter, a super genius, and so beloved by all that when he falls ill, the entire planet, including countless tribes he has never met, is worried sick about him. Some of them add him to their pantheons.
Heck — his middle name is "Goodboy"! Lafayette, dontcha think you were trying a mite too hard to make this guy a God among men?
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.
Alternate 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 backwards slaves, whose masters invaded Earth 1000 years ago, 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.
Bile Fascination: The movie regularly places in the top (bottom?) 10 of most filmgoers' "worst movies of all time" lists.
Crowning Music of Awesome: Elia Cmiral'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.
Ho Yay: One of Jonny's followers spends much of the movie looking soulfully at his leader. Jonny even cuts off a lock of his hair for him, and he wraps it around his fist as a sort of talisman. There's arguably more chemistry between the two than between Jonny and his designated love interest.
The Rifftrax guys had no trouble picking up on this subtext. Whenever the guy makes puppy dog eyes at Johnny, they start tearfully muttering "Love you!"
Idiot Plot: Characters aren't making the wisest decisions in this film. Heck, the whole plot is kicked off, and Johnny's plan works, entirely because Terl is a greedy moron.
Nausea Fuel: Given the amount of tilted camera shots, it's probably a good idea to avoid this movie if you suffer from motion sickness.
The entire film seems Hellbent on making the viewers as queasy and uncomfortable as humanly 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.
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.
Special Effect Failure: The movie has a few scenes that fall under this trope. But the most infamous example would be 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 an invisible string.
Semi-averted with the alien who built the Instant Expert machine. The book calls the race Chinkos, and you suddenly realize the entire race is a caricature of the Chinese. The movie changed the name of the race to "Clinkos" and kept its role minimal, except for the fact the Clinkos still have offensive Asian stereotypical behavior.
As Cracked.com has put it, "It is important to note that the feel-good ending of the film is when someone destroys the decadent capitalist empire with suicide bombing." And moving backwards with this thought in mind, it is disturbing to see the things the heroes go through, like learning to fly planes from the enemy, and building up a (near-)quasi-religious-fanaticism, to attain their goal.
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) actually manages to be pretty spectacular.