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: The Bell Jar
Harsher in Hindsight: Whenever anyone talks about Sylvia Plath's suicide at the age of 30 (only a month after the book's initial publication), you can expect someone to mention this particular quote from the novel: "How did I know that someday—at college, in Europe, somewhere, anywhere—the bell jar, with its stifling distortions, wouldn't descend again?"
Les Yay: Esther discovers Joan and DeeDee in bed together. Joan tells Esther that she likes her more than she likes Buddy.
Subverted: Esther then immediately tells Joan she hates her, which makes Joan commit suicide
Tear Jerker: If you can relate to Esther, then you may get teary-eyed as her condition worsens.
True Art Is Angsty: Not as soul-crushingly depressing as other examples of the trope as the ending gives the impression that Esther will be okay and the novel can be comforting to some people.
Vindicated by History: Initial reviews weren't particularly generous; now it's taught in high schools and colleges.
What Do You Mean, It's Not for Kids?: Just as studying William Shakespeare might put you off his plays for life, having to analyse Sylvia Plath's poetry in detail was the bane of some UK students' A-Level years. These poems are definitely not for anyone younger than 16, either.
Some younger readers might be put off by the scene immediately following Esther's deflowering, where she suffers massive bleeding, and Joan can't find a doctor because it's the weekend. Once she gets to an ER, the doctor fixes it easily. He doesn't say what the problem is, but she probably had a rupture in a small artery.
The Woobie: Esther and Buddy. Esther's an understandable Woobie while Buddy's more subtle. Think about it: he has TB and his girlfriend's happy about it, he has a painfully honest understanding that part of his appeal is his attractiveness, and Esther basically rejects him on the grounds of him giving an actually honest answer to her personal question of him having an affair (though that doesn't negate the fact he still had one...) They appear to come to.
Not to mention that he did actually respect Esther much more than she lets on, taking her to the hospital when his colleagues thought women shouldn't be allowed in. And the fact he actually tried to understand her (by writing poetry) and be romantic. They seem to have something vaguely resembling a reconciliation at the end though.
Buddy: Let me fly with you.
Later, when she along with Joan were sectioned, he was frightened he drove women crazy.