What makes Don Draper, in my opinion, one of the most interesting characters on TV in recent years is how morally ambiguous he is. He is cynical, arrogant, vindictive, manipulative, unfaithful, and hypocritical. Yet he is also capable of committing extremely noble deeds, of being protective and nurturing. His best work as an advertising creative shows that all human desire is anchored in love. His cruelest acts are done with neither hesitation nor guilt. He is at his most creative when he is also at his most destructive. He is most powerful when he is most broken.
The complaint I heard most about Mad Men's Season 5 was that Don Draper in love and happy was but a shadow of the self-loathing juggernaut of a man from the previous seasons. That season ended with Don diving back into the cesspool of deceit that is his natural element.
But then the complaint I heard most about Mad Men's Season 6 was that Don took to the nastiness a little too well, outdoing every despicable thing he'd done in the previous seasons. I must admit that I was turned off by the character a few times in this season. But then the final scene of the season ender made it all worthwhile.