I avoided Uncle Tom's Cabin for years anticipating caricatures, bad writing, and preachiness. Frankly, it was much better than I expected. Yes, there are some stereotypes, but there are also many nuanced, well-drawn characters. I had to read all 300 pages before I could decide in which group to fit Uncle Tom. It would have been easy to write off him for his unusually placid outlook on life, which is why I think Stowe was wise to create a needed contrast in the character of George.
Sometimes Stowe was preachy, but she also worked hard to show different points of view on slavery. It was fascinating to see every possible Scripture verse (both to defend and denounce it) coming out of the mouths of the main characters. Some, like Maria, hold to their views of slavery no matter what they see with their own eyes. Others, like Ophelia, grow in their understanding of the problem. Though Ophelia is convinced that slaves have eternal souls and should be educated and treated well, she is initially horrified when Eva kisses one of the black servants. She slowly evolves, becoming a tender and true woman of faith.
Three drawbacks: Stowe, in her effort to be gracious toward blacks, unknowingly writes condescendingly, often making blanket statements about them as "a sensitive and impressionable race," or describing a person as acting "after the manner of their race." It doesn't wear well today, but I'm sure that at the time of her writing, it was seen as sympathetic. Also, the "N" word is used frequently by both whites and blacks. Last of all, the saintliest person in the book was, to me, the least believable.
I was intrigued by the fact that even though slavery was the primary issue in the novel, a strong secondary theme was theodicy. Is it possible to trust God in the midst of extreme suffering? Very thought-provoking!