Is it fair to say that Macbeth's change in character is more dramatic than that of any other Shakesperean tragic hero?
It is, I think, fair to argue this point. Even without comparing Macbeth to other Shakespearean characters, the change in Macbeth is striking. At the beginning of the play, he is portrayed as a hero and a good vassal to Duncan, slaying the king's enemies (albeit, ominously, in a very bloody fashion) and saying all the right things about duty and service. Even after the witches' prophecy, he requires the goading of his wife to push him toward committing murder, and is torn by his conscience for the first three acts. Yet by the end of the play, we see that Macbeth has become an almost remorseless killer, one who can casually order the deaths of Macduff and his family. Shakespeare uses Macbeth's character to show the ways in which ambition, once piqued, can destroy the good in us. Again, Macbeth is not the only Shakespearean character who goes through major change: both King Lear and Prince Hal/Henry V spring immediately to mind; but the alteration in Macbeth's character is profound. It is Shakespeare's great achievement to highlight how this change occurs. A man who Banquo could ask "why do you start, and seem to fear / Things that do sound so fair?" when he hears the witches' prophecy is obsessed with his own power by the end of the play.