I beg to differ with the above comment.
Macbeth is a tragic hero and the beginning praise by Duncan about his military skills proves it. Also, in regard to the witches, they merely predict what will happen, but never are we given the impression that the witches have actually INFLUENCED Macbeth to do anything. So yes, the methods and ideas are from his own mind, but what do we see throughout Macbeth?
We see a man, once noble and honorable, praised by the king, a cousin of him as well, suddenly sell his humanity to ambition.
...I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o'erleaps itself
And falls on the other.
He knows what he's doing and he's in full control, but we see the struggle in his eloquent poetry. We see the conflict between his moral self and his ambition. Ambition wins out, and Macbeth embraces immorality.
Once he gets what he wants, the crown, he realizes he is not happy. He can't trust anyone, and no one will trust him. His wife is mad, and a lot of people are...well, dead. This is his reversal of fortune.
Macbeth soon loses his vigor in the speech in Act V Scene V. (too lazy to quote it. *sweatdrop*) where he speaks of how futile Life is.
Macbeth is a tragic hero through and through. However his actions cause resentment amongst the audience, so instead of feeling sorrow at his demise as we would for Othello, Hamlet, or King Lear, we feel relief that such a tyrant is dead. But in truth, there was a story, there was a human inside this tyrant. He is literary proof as to the dangers of ambition.