Re: Sylar - what wee_warrior said, plus:

I still don't think that Sylar's sudden guilty conscience about the prospect of killing "innocent people" makes sense in context of the way his characters has been presented so far.

Oh, that wasn't the impression I got. I thought what confounded him wasn't "why would I kill these innocent people" but "why would I kill these people when I have nothing whatsoever to gain from it?" Considering all his previous kills gave him something, that was in character, and not a guilty conscience. Then, after his mother's death, his last vision obviously showed him that the President he already painted is himself, as a direct consequence of the nuclear explosion. After which he knew what he had to gain.

Also: bringing Molly back, who lost her parents because of Sylar and would have been dead herself if he had found her, reemphasizes the humanity of his victims again as well.