This is a very good question.Macbethis essentially nothing more than a story about a ruthless, ambitious murderer. Shakespeare'sRichard III, it is worth remembering, is also a story about a ruthless, ambitious murderer. What savesMacbethfrom being nothing more than such a story, in my opinion, is the beautiful language that is used in many places throughout the play. Some passages are among the most beautiful Shakespeare ever wrote. Here is one example from Act 2, Scene 2, right after Macbeth returns from murdering Duncan:
Methought I heard a voice cry "Sleep no more!
Macbeth does murder sleep"--the innocent sleep,
Sleep that knits up the raveled sleave of care,
The death of each day's life, sore labor's bath,
Balm of hurt minds, great nature's second course,
Chief nourisher in life's feast.
Then in Act 5, Scene 3, when the Doctor tells Macbeth, in effect, that Lady Macbeth's illness is psychological, Macbeth replies:
Cure her of that.
Canst thou not minister to a mind diseased,
Pluck from the memory a rooted sorrow,
Raze out the written troubles of the brain,
And with some sweet oblivious antidote
Cleanse the stuffed bosom of that perilous stuff
Which weighs upon the heart?
The story is just a sort of framework on which Shakespeare displays his poetic genius. People have read Macbethover and over again, and watched different performances of the play, not because of the story but because of the language.
Tomorrow and tomorrow and tomorrow
Creeps in this petty pace from day to day
To the last syllable of recorded time,
And all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more. It is a tale
Told by an idiot, full of sound and fury,
(Act 5, Scene 5)