What is the greatest weakness of the book, The Adventures of Huckleberry Finn?

Many readers and literary critics are disappointed in the last episodes of the book.  The episode begins when Huck pretends to be Tom Sawyer because Aunt Sally is expecting Tom to visit the farm.  When the real Tom arrives, he cleverly goes along with the ruse, and in his adventurous spirit, locks up Jim in a shed.  Even though Tom knows that Jim is a free slave, he “tortures” Jim with spiders, rats, and snakes....

Many readers and literary critics are disappointed in the last episodes of the book.  The episode begins when Huck pretends to be Tom Sawyer because Aunt Sally is expecting Tom to visit the farm.  When the real Tom arrives, he cleverly goes along with the ruse, and in his adventurous spirit, locks up Jim in a shed.  Even though Tom knows that Jim is a free slave, he “tortures” Jim with spiders, rats, and snakes.  Everything works out in the end, and Tom admits that Jim is free, but it is still a part of the book where readers tend to “scratch their heads.”  Right before the episode, Huck has an epiphany about Jim and decides to tear up the letter he writes to Miss Watson telling her that he has Jim.  Huck has learned to love Jim as a friend and father figure.  Because Huck goes along with Tom’s pranks, many readers are disappointed in Huck’s decisions.  It seems to be out of character from the heroic Huck we just recently cheered for. 

As a teacher, I have read many critical essays about the last episode.  There are a lot of theories by famous Twain historians like an old professor of mine, Tom Quirk.  Many scholarly people want to understand what Twain’s intentions are at the end of the novel.  One critic I read said that the end of the book is symbolic of Reconstruction and is shown through how Jim is politically free but not socially free.  It’s an interesting idea. (Sorry, I can't remember where I read this!)

However, overall, many readers feel that the behavior and acts of Huck Finn at the end of the novel is disappointing and a flaw of the novel. 

Here's a good reference for you.  

Quirk, Tom. “The Flawed Greatness of Huckleberry Finn”  mizzou.mag.missour.edu May 21, 2013