Amazing episode, although I find it odd that so many reviewers here didn't catch onto the fact that Walt called his wife a "stupid bitch" because he was trying to protect his family.
He consciously kidnapped the child so that the police would arrive at the house and tap the phone. He then called, knowing that they were listening in (and asking "are you alone?" to make the police believe he was being honest), and then tried to give the impression that he had held his wife under duress the whole time. He pinned all of the blame on himself to save his family, and it draws such a strong connection to the first season, where he explains that family is everything. Shrouded in guilt and blood, he's returned to his original values.
I will be hard pressed to find such a whirlwind of a show when I'm done with this. Truly incredible!