I think the biggest strength of Macbeth that is also shown to be a weakness in the final act of this amazing tragedy would be his confidence, which borders on arrogance. Macbeth's problem is that he places too much faith in the prophecy of the witches, and as a result, he is brash and over-confident as he contemplates Malcolm's attack of his castle. Note what he says at the beginning of Act V scene 3 and the tone of his speech:
Bring me no more reports; let them fly all:
Till Birnam wood remove to Dunsinane,
I cannot taint with fear. What's the boy Malcolm?
Was he not born of woman?
Let us remember that prior to the beginning of this scene a messenger has obviously brought him news of desertions of his lords and soldiers to Malcolm's side. Even though in reality this leaves Macbeth in a very vulnerable position, which should concern him, the prophecy gives him a real sense of arrogance that is his downfall. Although on the one hand it is a definite strength that he is brave and unaffected as a leader by these desertions, it also leads him to believe he can be victorious over any opponent, no matter how many of his men and lords desert him.
I remember watching the Polanski version of Macbeth as a teenager. I thought he did pretty well kicking young Siward's behind and that he could have even "taken" Macduff if he wanted to. Here is the thing, I don't really think that Macbeth wanted to live by the end. Macbeth was way too emotional for his own good. It's one thing to want to kill lots of people to be King and another thing to want to die when you get there. Macbeth never could calm down. Sure his passion could help him but it was also his undoing.