Firstly it needs to be said that Polanski is a talented director whose movies are veritable works of art. However, when one decides to alter Shakespeare one draws upon oneself a certain attention and criticism in terms of whether that change was necessary to begin with. There are several differences between Polanski’s Macbeth and the original, but the most obvious ones are of course the conversion from soliloquy to monologue for the sake of psychological sense and continuity within the movie. Furthermore, there were quite a few lines that got rewritten, which makes sense bearing in mind that the original play was written in modernly incomprehensible Shakespearean English. Also, quite a few scenes were not shot at all as they were considered trivial in the larger image. There were also changes that can be considered to be flat out mistakes such as the lyrics to the song sung by Fleance at the banquet that Macbeth holds for Duncan at Iverness.
Furthermore, the Polanski version makes the assumption that all royalty is doomed to fall into the same sequence of traitorous events. That is why the ending to Polanski’s version shows Donalbain seeking the witches’ counsel, presumably to usurp Malcolm in the same manner that Macbeth did to Duncan. This implies that the cycle can and will repeat itself ad infinitum. What’s truly fascinating about this version is that Polanski’s Macbeth is more of a historical work than a dramatic one as it does not try, beyond reason, to tragically paint these historical figures. Rather, it attempts to stay as grounded in reality as possible, thereby displaying the many negative sides to humanity and royalty, specifically in the middle ages.
I suppose that while rewriting plays of this caliber the most important thing to remember is that critics will always wonder whether or not the latter version were necessary, but Polanski does not suffer from this issue, probably because he does such an effective job portraying his characters as both tragic and cinematic. In fact, the cinematic aspect of this movie makes for a very easy to view the movie that can be followed easily and coupled with the simplicity of the language, it’s basically a very effective Shakespeare cover.