These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternative Character Interpretation: As usual with Shakespeare, there are an absurd number of ways everyone can be portrayed, and which comes across most strongly depends in large part upon the production or the reader.
Macduff appears to be the valiant hero of the play, and yet he leaves the country to find Malcolm when he must know that by doing so he not only leaves his family more vulnerable, but gives Macbeth the suspicion of himself that causes him to murder them in the first place.
The Complete Pelican Shakespeare includes a fascinating essay before each play, and the one for Macbeth paints a convincing portrat of a noted alternate interpretation of Duncan, which is that he plays the saint but is in actuality a cunning bastard who killed and cheated his way to the top and is merely feigning a belief in the divinity of his family's kingship. The essay specifically compares him to Edmond from King Lear in a scenario where Edmond survived to an older age.
Roman Polanski's film interpretation has a rather cynical interpretation of the characters Ross and Donalbain.
How about just throwing out the play's depiction of the witches as crones and interpreting them as standard Hecate Sisters?
After all, their name is mentioned several times in the dialogue.
Was Duncan a good king or was he just a tyrant and everyone else who were loyal to him just loyalists?
One-Scene Wonder: The Sergeant only appears in one scene in the entire play, but his speech to Duncan—where he recounts Macbeth and Banquo's victory on the battlefield—is considered one of the play's most memorable monologues.
The Scrappy: Hecate, for many (see Fanon Discontinuity). Part of the reason that many productions cut her out (in addition to the theory that Shakespeare didn't mean to include her) is that she just doesn't serve any clear narrative purpose, and that her dialogue is composed entirely of forced, awkward rhymes.
Squick: Lady Macbeth's remark about smashing an infant's skull after ripping it from her breast.