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.
Complete Monster: Bob Ewell: racist, abusive father, and attempted child murderer. He condemns an innocent man to death to try and avoid the shame of his daughter's sexual advances towards a black man and to prevent the brutal beating he gave his daughter after he walked in on said advances from being made public because he knows that Maycomb County's racist population will play along. And later, after he is publicly humiliated in the wake of Tom Robinson's trial, he lashes out at those involved with the trial, and among other things sexually harasses and yells obscenities at Tom's recently widowed wife, breaks into the judge's house with the implied intention of lying in wait to ambush him, and attempts to slit Scout and Jem's throats with a switchblade as they walk home from a school play.
In the film at least, after Atticus has brought the news of Tom's death to his family, Ewell has the gall to call Tom's father 'boy' and order him around. And the father has no choice but to go along with it.
Mayella definitely implies that he sexually abuses her.
Jerkass Woobie: Mayella is not a likable person at all, but it's extremelydifficult not to feel bad for her and understand why she's a less-than-pleasant person, and hope she can grow up and somehow turn her sad life around once her father gets what he deserves.
One-Scene Wonder: Boo Radley, as played by Robert Duvall, in his first film appearance ever. He is onscreen for just a moment, and doesn't utter a single word the entire time, but manages to say everything he needed to only using his eyes.
Some Anvils Need to Be Dropped: Treating people unfairly because they have a different skin color from you is wrong. A similar moral in empathy is dropped with Boo Radley, who is shunned for being different.
Also Consider The Source. I mean, anyone thinking rationally would take a second look at the accusation of Tom Robinson.
It's hypocritical to defend one group from persecution and then persecute another, as shown when Scout is utterly confused when her teacher talks about how horrible Hitler is for his mistreatment of the Jews, but had cheered on Tom Robinson's death sentence and then insulted the African American community at large.
Scout's Aunt's church group sneering at the African-Americans while bemoaning how the native Africans live in "sin and squalor" and need to be evangelized.
She was often accused of not writing this one (especially since her "childhood friend" was a bestselling author in his own right).
Values Dissonance: Examined. The teacher Miss Caroline is quite displeased that Scout learned reading at a young age because it goes against the school system.
The Woobie: Tom Robinson. He's a nice quiet family man who minded his own business, and occasionally helped Mayella. Nonetheless. Bob Ewell decides to get him killed.
Also, Tom's wife. She does her best to make ends meet for her children after her husband is framed and killed, only to be endlessly harassed by Bob Ewell and considered to be living in "sin and squalor" by the local white women.
As noted above, Mayella could be considered a Jerkass Woobie. Yes, she caused the court case, but she tried to seduce Tom because he was the only person who ever showed her any sort of affection or kindness and it's implied that she only goes along with the rape story because she's terrified of her father and because she just wants some kind of acceptance in the community.