No wonder Mansfield Park makes critics beg for the typical "bright and sparkling" Austen. If the description of Fanny's eight years of deprivation from love and affection don't make you close the book in tears, try to get through any scene where Mrs. Norris Breaking Speeches her, or the scene where she sits in the East Room having a breakdown over the loneliness and sense of zero self-worth that's built up over her life.
The scene at Mr. Rushworth's estate, where everyone keeps more or less abandoning Fanny in the woods (even Edmund, normally so attentive, actually forgets she's there), is really hard to read. It's especially painful since some of the characters make it clear that they're not particularly pleased with her for being where she is.
Sir Thomas, who had been noticeably kind and attentive to Fanny since his return from Antigua, absolutely lights into her for turning down Henry Crawford's proposal without even attempting to understand why she wouldn't want him. And having driven her to tears, he sternly orders her to pull herself together already and try to behave rationally. Fanny, being Fanny, considers that he's right in the latter and wonders if she really is being horrible and ungrateful even with all of her objections to Crawford's character.
When Tom is struck deathly ill, Fanny desperately wants to return from Portsmouth so she can be of assistance. But she doesn't even ask in her correspondence with Edmund. She's been so conditioned to believe in her own insignificance that she assumes it would be selfish of her to ask—and the Bertrams are so used to ignoring her that they don't offer, even though she would be helpful.
The discussion of slavery is a bit more explicit. Then Fanny curiously peers through Thomas Jr.s book and finds it rife with horrific imaginaries of torture and rape. His father tries to excuse it as just madness. The auditory screams heard in the music doesn't help.
Fanny returns to her childhood home and finds it just as poor and dilapidated, her father drunk, her siblings unmanaged, and her mother run ragged and unable to cope. Fanny is torn with the dilemma of whether or not to marry Henry Crawford even though she doesn't trust him. Mrs Price appears in the doorway after one of his visits and simply tells her, "Remember, I married for love."