I recently realized I could watch Mad Men season 6 online, but only for the next few weeks, so Sarah and I raced through season 5, which I guess we'd forgotten about. (If Matthew Weiner ever reads this blog, then he'll have to take that backhanded compliment.)
Now, there's a lot that goes into a show that we don't even notice until it goes wrong, which includes everything from the technical side to the research side. (Historical fiction is hard.) Conversely, there's all the flashy acting that we see, which rightly gets a lot of attention. So much of the action of Mad Men takes place on Don's face. And for all that we have a romantic view of writing as a personal expression of one person, we have to recognize the collaborative efforts that go into this sort of work.
This goes doubly, probably, for a show that skirts the edge of being an ensemble. Sure, the argument could be made that Don is the protagonist or that he shares the role with Peggy--her rise contrasted with his fall, a la Dreiser's Sister Carrie. Really--and spoilers abound from here on out--so many of the main characters get some arc or moment to shine, dramatically, whether it's the ongoing money troubles that lead Lane to embezzlement, which leads him to suicide; or the less-defined arc of Roger Sterling dealing with the emptiness of his life.
Looked at as a serial, one of the benefits of this ensemble cast is that you can seed elements in in small portions. So we don't have an entire episode dedicated to Lane's money troubles until we've seen a little issue here and a little issue there.
There's also something to be said for the ensemble cast providing multiple points of view: Roger Sterling is always ready with a quip, but he'd make a terrible viewpoint character because his selfishness makes him hard to relate to; we get to see Peggy's triumphs and lows contrasted with Don's, both in work and at home; Stan may be a relatively minor character--we don't learn much about him--but he gets to sit in on the meetings and voice the viewer's thoughts without having to embody all of the viewer's issues (which he couldn't because he's from a different time period); etc.
Which brings me to my final thought (in this first batch of thoughts), which is that Mad Men excels at mixing tones: tragedy and comedy, light and dark, satisfaction and creeping desolation. So in almost any scene, there's a certain ambiguity about whether it will turn out for the better or for the worse for the characters.