He has a fatal character flaw (hamartia): his ambition
Despite his hamartia, the audience does feel some sympathy for him
He is doomed to die at the end of the play
Macbeth at the beginning of the play
Brave: he is shown to be a fearless warrior (an "eagle" and a "lion" in battle)
Noble: it is reported that he has killed a traitor in battle, showing his loyalty to King Duncan and Scotland in general
Ambitious: unlike his comrade Banquo, he is easily seduced by the witches' dangerous prophecies
Conscientious: he questions the morality of committing regicide, which leads Lady Macbeth to challenge his courage and manliness
For Macbeth
There is a tension between the heroic and loyal aspect of his character and the ambition. This results in him questioning his actions repeatedly, but ultimately succumbing to his darker desires
Macbeth as the play progresses
Cruel: he murders his best friend, Banquo, and the wife and children of Macduff
Paranoid: he begins to suspect even innocent people are threats to his power, and even stops sharing things with Lady Macbeth ("full of scorpions is my mind")
Guilty: his hallucinations represent his increasing feelings of guilt for the regicide and murder of Banquo
Masculine: he becomes the cruel, violent man that Lady Macbeth accuses him of not being, and becomes the dominant force in their relationship
Nihilistic: ultimately, he questions the pointlessness of life. For a Christian, Jacobean audience, this would be seen as disturbing
Despite his hamartia, and the barbaric villain Macbeth becomes, there are still reasons for an audience to feel sympathy for him
Reasons for audience sympathy
He is tempted by evil witches
He is encouraged by a thoroughly unnatural woman, Lady Macbeth
He is thoroughly human: he is not pure evil, but a mixture of positive and negative character traits
His emotional reaction to his wife's death and questioning of his own actions as a result (Act V, Scene V)
Even at the end of the play, he dies a warrior's death, which could be seen by a Jacobean audience as heroic