I enjoy Flannery O'Conner but many don't because she writes a lot about some darker parts of human nature. I recommend you read "good country folk" and "a good man is hard to find", these are short stories and would be a good indicator of if you want to invest more time in her or not, She is completely an American writer, she captures life in the South and the mindset many have there perfectly.
I also am really getting into Ralph Ellison, read "Battle Royal" it's a short story that opens up the book "Invisible Man" This story is also strongly American (in the mid 20th century) and could not be transferred anywhere else, he writes from the point of a young intelligent African American man with high hopes and potential who gradually realizes the reality of the society he lives in.
I also like William Faulkner "A Rose for Emily" This is a commentary on the civil war, which was began largely due to racial issues.
These authors are symbolists and use metaphors a lot to examine things like American society and religion. The main differences I have seen are topics on racism, especially white/black and in the Faulkner story (North/South). America is such a conflicted place with so much space filled with many different cultures to the point that you can feel like you're in a different country depending on where you go, especially North vs. South. I am very naive about Europe, but I get the idea that in England the culture is more homogenous (as in people being similar no matter where you travel), I'm sorry if this a generality, but most English novels I have read come from a similar viewpoint, where America has so many different viewpoints because it has such a crazy history, and the novels are full of conflict because there are so many people fighting for different things.