Film "Scotland, PA" interprets Macbeth. How do the devices of cinema limit/enhance the meaning of the play, or the adaptation of tragedy into...

First, I just want to tell you that I love the movie, "Scotland, PA".  My biggest complaint is the quite liberal use of foul language.   The devices of cinema - camera tricks and cinematic effects - lend themselves very well to this play since the play deals with witches and spectral visitations.  In the play, the witches appear and disappear, Banquo's ghost is seen only by Macbeth, the witches conjure images for Macbeth to see and hear.  Obviously, a stage play will have problems showing those things that a movie can do so easily.  Also, it isn't difficult for a movie to show simultaneous action with quick segways from one scene to the next.  Act 5 of the play is a constant change from inside Macbeth's castle to outside the castle showing action as it occurs at the same time in both places.  Again, stage plays have more difficulty with this rapid and frequent change of scenes.  In "Scotland, PA", the witches (3 60's era hippies) do very little magic.  They do appear and disappear and show themselves only to Mac McBeth.  There are no visitations as dramatized in Act 4, sc. 1 of the play, though I wish the screen writers would have put those in there somehow.  There is the rapid switching of scenes in the final act and that is done well.  As far as changing "Macbeth" the bloody tragedy into a comedy, the film makers succeeded quite well.  The devices of cinema allowed for subtle expressions on faces that a stage play could not employ.  One particularly good example of the subtle expression is the look of relief on Pat's face when she cuts off her hand.  "Scotland, PA" is a black comedy because it bases its comedy on the horrific acts of Pat and Mac McBeth, from accidentally pushing Norm into the fryer (even though they were going to kill him anyway) to showing the hole left by the shotgun blast that killed Banquo, to the deaths of Mac and Pat.  The film does an excellent job of capturing some stereotypes which also adds to the comedy (the blundering small town deputy, the boozing guy pals, etc.).  The play is about unchecked ambition and what happens when a person does not let his sense rule over his base desires.  The theme is timeless and the movie helps to show that.  The movie also does a very good job of showing how the McBeths (the Lady Macbeth character, in particular) justified what they did.  In the play, Lady Macbeth justifies the killing of Duncan by claiming that her husband deserved to be king.  In the movie, Pat McBeth says that she and her husband aren't bad people, they are just underachievers.