This movie should have been a classic. It looks like it stayed close to the true events that happened and didn't 'Hollywoodize' it like they did in Mississippi Burning. Matthew McConaughey gives a pitch perfect performance as Newt. I can't imagine anyone doing it better.
Everything about the film- the locations, the actors, the script, the story itself is all first rate. It does lag a bit in the last 40 minutes, but I find that more emotionally moving than the well done battle scenes that make up the first 2/3rds of the film. The black actress in it was excellent too (didn't catch her real name).
I think the reason it didn't do well in the initial release is it isn't your typical North Versus South movie or white versus black- it is more complex than that. It deserved a lot better of a reception.