How can I compare Shakespeare's play Macbeth to its screen version by Rupert Goold?

First, you can examine the role played by the Weird Sisters in each.  In the play, they only appear in a few select scenes; however, in Goold's film, the sisters are much more pervasive and active.  For example, they show up in the scene where the captain speaks to Duncan to tell him about Macbeth's bravery in the field.  In this scene, they appear as nurses who then kill the captain when no one is watching.  Further, they appear in Macbeth's kitchen, helping to prepare the foods for the dinner with Duncan, and they reappear as servants at the dinner party where Banquo's ghost shows up.  They seem a great deal more evil, even more malicious than they do in the play, and their influence on Macbeth feels that much more omnipresent. 

Second, you could discuss the way the play has been updated in the film adaptation.  Instead of being set in Scotland in the eleventh century, the movie takes place in what seems like a twentieth century totalitarian country like Communist Russia or Nazi Germany.  This makes it feel somewhat more understandable to a modern audience, as we are a great deal more familiar with the way this symbolism and propaganda looks than we could be with Scotland of a millennium ago.