Probably the most notable difference between the film and the play is that the role of the Scottish King Macbeth is played by an African American. Not only that, but Macduff, his wife, and their son are played by Black actors.
Coen wasn't the first director to famously do a diverse production of Macbeth, as Citizen Kane director Orson Welles notably adapted and directed the play with an all-black cast back in 1936. But while Welles's version had the story set in Haiti, Coen's adaptation set the story back in Scotland, making the latter's diverse cast all the more remarkable. Nevertheless, when talking about the film's cast, Denzel Washingon said, "in my humble opinion, we ought to be at a place where diversity shouldn't even be mentioned, like it's something special."