Macbeth (the character, not the play) may be Shakespeare's best example of a tragic hero--an essentially good, noble man with a tragic flaw. Actually, Aristotle said the the ideal tragic hero was a man in whose character good and evil were mixed, but in whom the good predominated, and that description fits Macbeth even better. At the beginning he's a loyal officer fighting the enemies of his King and cousin, Duncan. However, when the witches greet him as Thane of Cawdor and then predict that he will be King, the latent evil in him begins to rouse. He learns almost immediately that he IS Thane of Cawdor, and that fact makes him give more credence to the other prediction--to the extent that he sees Duncan's proclamation of Malcolm as his heir an obstacle to be overcome. (Keep in mind that the Scottish crown at that time did not automatically pass from father to son, so that Malcolm did not represent an obstacle to Macbeth's succession until Duncan made that proclamation.)
Finally, Aristotle said that a good tragedy should elicit two emotions in the audience: :pity and fear. Therefore there must be something pathetic in a good tragedy, and Macduff's family is an excellent example. As for fear, the fear that Aristotle meant was a "There but for the grace of God go I" kind of fear--the fear that, if the viewer weren't careful, he might make similar mistakes and such a downfall might happen to him. The average person in the audience might never have the opportunity to rise to such heights if he would just rub out someone, but many of us have the opportunity to gain something if we would just do something unethical.