I just saw this film today and found it very powerful and entertaining. I have to say, the most powerful scene for me was near the end, the climax of the film, when Mary Surratt is told by her defender, Frederick Aiken, that she will be granted a new trial, a civilian trial with a jury of her peers. One problem is that the jury is made up of military generals who understand Lincoln's assassination was because of the Union victory in the war, and they want vengenace for this politically-motivated death. Mary Surratt becomes a pawn.
But she then learns that she will be hanged after all, because the president (Johnson) has decided to override the writ that granted the civil trial. After a difficult trial and the revelation of many examples of self-interest and dishonest behavior, this seeming example of justice feels like a victory; but, tragically, it is short-lived.