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.
The original literary series
Cult Classic: To the point that there are even people in the world who try to model their life on the ideals presented in the series.
We never see an old slavegirl. Slavegirls on Gor are primarily sex slaves, and can be killed for failing to please. Perhaps they're euthanized when their looks start to fade?
They supposedly have anti-aging treatments that prolong human life for centuries if not indefinitely. So, their looks might not fade for a long time. Of course, they're instead stuck in a life where they're used as human sex toys for multiple human lifetimes with little chance for freedom and the ever present fear of death by capricious jerks and likely conditioned to enjoy that sort of life, which is probably even more horrifying.
Curiosity and emotional control are stamped out of slaves, and they're also forcibly given birth control. So in essence, being a slavegirl is a form of physical and mental Creative Sterility.
While the phrase "Curiosity is not becoming in a slave girl" is a common one on Gor, nobody really believes that they shouldn't have any curiosity or emotions. Stupid girls don't make good slaves.
Ho Yay Shipping: Some readers find men embracing men automatically homosexual, so they get a lot out of the books.
Internet Backdraft: In 90% of the internet, a mention of Gor is equivalent to trolling, unless followed up with scathing hatred and opening the floor to burn John Norman in effigy. It is a banned topic on the StarDestroyer.net forums.
Jumped the Shark: Some will say that the shark was jumped by page 1, but a not-uncommon sentiment is that "the first N books aren't that bad..." for values of N that range from 2 to 6.
Marty Stu: Tarl is one of the most obvious ones ever.
Somewhere out there is a fan novel called Transvestites of Gor with a followup called Female Men of Gor. Fans at conventions used to joke about Podkayne of Gor, but it's uncertain whether that one actually exists.
And indeed the Quotes section of this very page consists only of parodies, not selections from the books themselves.
Unfortunate Implications: Not so much implied as bashed over one's head. One standout is a black woman in Assassin who takes to slavery extremely easily, even by Gorean standards (the others comment on this).
Values Dissonance: Tarl expresses this himself throughout the first books, when he's still a Stranger in a Strange Land, less and less as he adapts. Then in the late series, he and a few other Masters clinging to their values refuse to see that the world is changing, and keep insisting that it's wrong.
A meta example: The loudest critics simply can't accept that they have Values Dissonance with a completely fictional culture, and analyze it with that in their perspective. And so they wage as much as The War on Straw over the books as John Norman does with the characters in it.
Take That, Scrappy!: Even the film seems to have been aware of just how annoying Watney was, as evidenced by the ending where the ring ends up sending Watney back to Earth alone without Cabot, who finally gets to be with Talena, while Watney ends up having to explain to some cops why he's jaywalking in the middle of Los Angeles dressed in a ridiculous outfit.