Except for the 1937 John Ford movie, THE PRISONER OF SHARK ISLAND, this film is the most centered on the story of the assassination of Abraham Lincoln. But that said, it misses the effectiveness of being definitive like Stone's interesting (if flawed) JFK. The film is based on Eleanor Ruggles biography (of the same name) of Edwin Booth's career. So the central figure is Edwin, probably the greatest American actor of the 19th Century. Richard Burton, as a growing Shakespearean actor, was perfect as the talented Edwin. His father, the talented but eccentric and alcoholic Junius Brutus Booth Sr, is played by Raymond Massey (ironically the same actor who played Lincoln in ABE LINCOLN IN ILLINOIS, and John Brown in SANTA FE TRAIL and SEVEN ANGRY MEN). As the egotistical John Wilkes Booth we have the young, still promising John Derek.
The movie only goes from 1852 (when Junius Booth died) through 1866, when the American public showed Edwin Booth that it did not hold him or his family guilty for the stupid, vicious act of his brother. It does not carry the story down to Booth's death in 1893, with his success as the definitive Hamlet of his age, and his failure as a theatrical producer. Edwin Booth worked until about 1891, due to the debts he accumulated. But his last years were stable, with his second wife. He also found time to create the Player's Club (still located in his Gramercy Park brownstone). Only the tragedy of the President's death at his brother's hands left a really brutal mark on him.
Derek does the most with his role - showing the strong desire for "real fame" that took control over John Wilkes. As his character kills the character played by Massey in one film, he ironically also attends the hanging of John Brown - historically correct. But his intricate plot to first kidnap Lincoln and then kill him, and his relations with other conspirators is not really gone into. Still, the assassination, chase, capture, and death of the assassin are done fairly correctly. But to get the tone of the government's prosecution of the conspirators, see John Ford's film.