Is kinda rare to see a female and male character fit so well on screen, Frances McDormand and Sam Rockweel perfomances are amazing, Woody Harrelson is also great, in fact everyone in this film is great, even the characters with short time on screen, that's great writing, direction and acting.
McDormand show extremely well the terrible weight and pain that her character is suffering, she also shows a lot attitude in the things she does and says, the way she walks and looks to someone is like she's going to war.
Rockweel also give the best performance of his career so far, he balanced being funny, dumb, racist, violent, weak and strong, he does all that extremely well.
Three Billboards Outside Ebbing, Missouri is a very good film and can become a classic on character development.