I thought that was the best episode in a while. It may have also been January Jones' (and perhaps Kiernan Shipka's) finest moment in the entire series and it put the Betty character into a context with which the viewer could empathize with her for perhaps the first time. It's easy to think of her in Don's words as "spoiled Main Line brat", but the conversation she has with Sally on the bed kind of makes you realize that she has fought for some things, especially to sustain/save her marriage with Don.
I'm looking forward to seeing what they do with the finale. Before this episode, I thought this season had been simply "okay", but I thought the same thing about Justified and then the final two episodes absolutely blew me away.