In what ways is Macbeth different to the man we saw at the end of Act One?

At the end of Act One, Macbeth is ruled and easily manipulated by his wife.  When he tells her that they "will proceed no further in this business" of killing Duncan, Lady Macbeth freaks out and begins to question his masculinity, claiming that he can no longer consider himself a man if he backs out.  According to her, she would kill her own baby if she'd promised him to do it before she would ever...

At the end of Act One, Macbeth is ruled and easily manipulated by his wife.  When he tells her that they "will proceed no further in this business" of killing Duncan, Lady Macbeth freaks out and begins to question his masculinity, claiming that he can no longer consider himself a man if he backs out.  According to her, she would kill her own baby if she'd promised him to do it before she would ever go back on a promise to him.  She attacks and attacks until he begins to break down, wondering what they will do if they fail.  Once she sees this crack in his resolve, she becomes cajoling and persuasive, insisting that if he will "screw [his] courage to the sticking place / [Then they'll] not fail."  And with that, she's convinced him.

However, by the end of the play, Macbeth no longer takes orders from his wife.  In fact, when he plans and executes (pun intended!) Banquo's murder, he doesn't even consult her -- in fact, he sort of lies to her; further, when she asks if he has anything planned, he tells her not to worry about it for the time being.  When she eventually takes her own life, he seems to have reached a certain level of resignation: in Act 1, he'd felt strongly -- whether it was that he ought to murder Duncan or ought not to -- but now he just seems like a pale shade of his former intensity and passion and fight.  He describes life as a "walking shadow" and "a tale / told by an idiot, full of sound and fury, / Signifying nothing."  He used to believe that fate had a tremendous purpose for him, that he would be great; now he believes that life really has no purpose and that, in the end, it really has no meaning at all.  He is, in many ways, a shell of the man he once was, having done so many terrible things in order to satisfy his pride and ambition, and yet he has never found happiness or contentedness from any of it.