The range and power of both actors is beyond anything I have seen in this season on Mad Men; some people are saying it's the best acting John Hamm has done in the whole four seasons. To some degree his task over seasons 1-3 was to convey with conviction a perfect icon, which occasionally showed cracks (like when he got smashed on the head). A mannered, formal performance. In this season the task has been much more demanding, more freeform, a man trying to maintain a threadbare façade with increasing desperation, and being constantly smashed.
And as an audience, in rooting for him, you have been rooting for successful continuing illusion. 'Fool 'em one more day, Don!' Every episode to date (I think this is right) ended with the image of a door slammed shut - another successful campaign to keep the world at bay. Another duck and dive.
In this episode Don got broken down, like Sonny Liston knocked out by Muhammed Ali. In this surrender, he was able to reverse. The key truth in Mad Men is that you have to go down, down, into darkness and authenticity, into what is down underneath appearances, in order to create new things. 'What is awful and what is good are very close together.'