Angst? What Angst?: Huck is very cavalier about his father's unavailability and drunkenness, his mother's apparent death, and the fact that he's living on the streets—in fact, when people attempt to give him the maternal love they believe he needs, he only gets embarrassed.
Sequelitis: Not for Huckleberry Finn, but the further sequels "Tom Sawyer Abroad" and "Tom Sawyer, Detective." Yes, those really exist. And they were written by Mark Twain himself, too. He lost much of his wealth in bad investments and he needed to support his family.
Unintentionally Sympathetic: Mr. Dobbins for some adult readers. When young he had very much wanted to become a doctor but was unable to continue his studies for financial reasons. Hence he ended up a country school teacher (which was not considered a prestigious job for men in the nineteenth century). He still enjoys reading his anatomy text, but then one of his students has the nerve to go through his desk and damage his book.
However, it is also highly implied that during school hours he reads the part of the book with pictures of naked women. In front of little children.
Adult readers also tend to find Aunt Polly much more sympathetic; for all her faults, she is doing her best to raise her nephew and two other children on her own. Further, she's subjected to the worst Adult Fear — the loss of a child — not once, but twice, in the course of the book; her emotional torment is all too clear, especially to readers who are parents themselves.
Values Dissonance: Beatings, whether at school or at home, were quite common, and Huck even states that his back doesn't mind any more.
Injun Joe has caused controversy too among modern readers. At least one animated adaptation even went as far as to rename its depiction of the character as "Tattoo Joe".
The Adventures of Tom Sawyer: The Musical
Crowning Music Of Heartwarming: "This Time Tomorrow" - a little song by Aunt Polly as she watches her nephew, musing over the growing process of children and assuring Tom that she will always love him.