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.
YMMV: Jane Eyre
Accidental Innuendo: Some of the dated language can bring this effect on us modern readers. One part in particular:
"The clock struck eight strokes. It aroused him; he uncrossed his legs, sat erect, turned to me."
Rochester at one point describes Blanche as an "extensive armful."
Alternative Character Interpretation: Some have interpreted Bertha's "insanity" actually being social mores that contrasted with their current society. Her violent tendencies were actually caused by being locked up in relative isolation for several years.
Ambiguous DisorderBertha. Some of her appearance suggests she's hypermanic, some of her behaviour suggests severe dementia, some of it is like very severe autism (though that was hardly going to have developed in adulthood. (It doesn't help that her description sounds like she's badly neglected- however difficult she is, Grace could at least do something with her hair.) Justified, as this was long before any modern language about mental illness was in use even by experts.
Designated Villain: Bertha. She's the main obstacle that stands in the way of Jane and Rochester's romance and she gets a Karmic Death at the end, complete with Rochester redeeming himself by trying to save her, yet her only "crime" is suffering from insanity.
Fair for Its Day: The novel is often taught as a proto-feminist work. This trope combines with Seinfeld Is Unfunny when modern readers react unfavorably to Jane's behavior, finding it not assertive enough.
Fridge Horror: The realization that Jane was physically and emotionally abused through most of her childhood is a bit disheartening.
Hollywood Homely: Rochester and Jane are described as "unattractive" and "plain", respectively, but both pass up on more attractive potential mates to be with each other. Most adaptations cast attractive actors anyway, with Rochester played by dashing older gentlemen and Jane played by attractive women in somber attire.
Ron the Death Eater - Rochester, who is surly and somewhat morally ambiguous, is often lumped into the same category as Heathcliff. This completely ignores the fact that Rochester is a moral guy who has made some mistakes over the years, and only puts up a Jerkass Faēade as a defense.
Uncanny Valley: Jane is the only person who recognizes that there is something wrong with Mr Mason.
Values Dissonance. Possibly the most blindingly obvious instance in 19th century English literature. Bertha Mason is shown as being evil beyond redemption because she is insane. Worse, the very first really humane asylums for the mentally ill were being opened at the time and place the book is set (Yorkshire in the 1810-1820 period). Rochester could have afforded to send Bertha to one out of his pocket change with nobody knowing who she was. Yet he instead kept her hidden in his decrepit attic in rags with only a drunken slattern as company, quite possibly a fate worse than death. Jane's acceptance of this explanation shows that she (and her author) were out of touch with the times: during the Enlightenment people started to reject the idea that people who were insane were morally degenerate and evil and that it was an illness that should be treated, however bizarre the treatments occasionally became.
Rochester's attempt to be humane itself causing Values Dissonance. Rochester thinks the location of his forestland house, Ferndean Manor, where he'll eventually live blissfully with Jane anyway, could potentially be fatally unhealthy for Bertha, but locking her up in a sunless attic cell is perfectly fine. Nowadays, the roles of solitary confinement and wilderness therapy are reversed. Arguably a case of Science Marches On, but independent of scientific thought, it shows how we've changed our values to regard "being close to nature" as a glowingly wonderful catalyst of healing, instead of a terrifying, sickness-inducing hazard to women.
"Humane" may be a relative word here—a lot of nineteenth and even twentieth century institutions still turned out to be pretty grim places. Hence, even if better asylums were starting to open, it's not inconceivable that some people would still think it preferable to keep an insane relative at home. Even today the decision of whether or not to put a family member in an institution can be a very difficult one.
"Sir," I interrupted him, "you are inexorable for that unfortunate lady: you speak of her with hate — with vindictive antipathy. It is cruel — she cannot help being mad."
Rochester insists that he doesn't hate Bertha because she's mad, she was just (apparently, if you believe him) that wicked.
Some of that was Brontė trying to make it clear that Bertha wasn't to be reviled because she was crazy. In later years Brontė spoke in several letters about wanting readers to feel pity, not revulsion, but never quite being able to create that in the writing.
When Jane suggest to St. John Rivers that he need not be a missionary to the East: "Relinquish! What! ... [My hopes] of carrying knowledge into the realms of ignorance — of substituting peace for war — freedom for bondage — religion for superstition — the hope of heaven for the fear of hell?"
Rochester dressing up as a fortune teller involves him darkening his face with makeup. This detail is removed in most adaptations and is a likely reason why the scene is often removed entirely.
The classic film starring Joan Fontaine as Jane and Orson Welles as Rochester. Co-adapted by Aldous Huxley, after his work on Pride and Prejudice: It's a bit hilarious seeing Joan Fontaine, one of the most gorgeous actresses even to grace the screen, declaring herself "plain and little." To say nothing of a young Orson Welles calling himself "as ugly as sin".
ITV's telefilm starring Samantha Morton (the 1996 Emma) as Jane and Ciaran Hinds (the 1995 Persuasion) as Rochester. Perhaps inverted this with casting the rough looking Mr. Hinds. However, Samantha Morton plays "plain and little" Jane while being arguably a world-class hottie.