How did Macbeth change to become more (or less) admirable?
Macbeth begins as a wholly admirable character. At the beginning of the play, his king and all his associates are loud in his praise. He has fought valiantly against traitors and has secured victory for his king:
For brave Macbeth—well he deserves that name—
Disdaining fortune, with his brandish'd steel,
Which smoked with bloody execution,
Like valor's minion carved out his passage
Till he faced the slave,
Which ne'er shook hands, nor bade farewell to him,
Till he unseam'd him from the nave to the chaps,
And fix'd his head upon our battlements. (Act I, Scene 2)
However, even at the beginning the evident interest the witches have in him signals that he may not be as good a person as he seems to be. When he first begins to consider "helping" the witches' prophecy to come true, this does not damage our admiration much. He does not fall to temptation easily, and the ardor of his wife for the murder of Duncan deflects much of our distaste for this action onto her. She frames a failure to act as a lack of manhood:
What beast was't then
That made you break this enterprise to me?
When you durst do it, then you were a man.... (Act I, Scene 7)
However, with the murder of Banquo, Macbeth launches onto an independent career as an evildoer, which he continues with oppressive rule over his country and such outrages as the murder of Macduff's family. Our estimation of him undergoes a further decline accordingly. Nevertheless, by the end of the play, his steadiness and resolute determination to sell his life dearly, and the way in which the witches have tricked him, win back a small measure of the admiration he originally received from us:
I will not yield,
To kiss the ground before young Malcolm's feet,
And to be baited with the rabble's curse.
Though Birnam Wood be come to Dunsinane,
And thou opposed, being of no woman born,
Yet I will try the last. (Act V, Scene 7)