So Mad Men is finally over, and the finale was, well, OK. Which is a bit of an anticlimax for a show that started off so very well. The best, I think, that can be said of the finale is that it could have been worse.
Several of the stories ended satisfyingly: Peggy and Stan are finally together, Joan is still trying to balance personal life with ambition, Pete somehow lucked his way into a new lease on life, etc. But Don's ending doesn't really work, and unfortunately that's the critical one.
The show's writers have said that one thing they really tried with this show was not letting the characters change too much. Sure, Don might go on the straight and narrow for a while, but you know he's coming back to his philandering ways soon enough. So at the end we see Don at a yoga retreat in California, presumably breaking through something in himself and starting anew. It's dawn, of course, with obvious symbolism. But this breaks the whole contract of the show. It's a happy ending, I suppose, but we can't really believe it.
The one thing Don is always saying is that he "wants to build something". But he never quite does - he's constantly hemmed in by the strings other people attach. He's also haunted by his own identity crisis, but he doesn't resolve this. (The crisis, by the way, is why the hypothetical ending in which Don switches identities again in order to start anew doesn't work: he hates himself for what he did. Doing it again would be even worse, and he knows it.) It would have been great to see progress on at least one of these problems of Don's, but we don't.
Endings are hard, so not failing is actually better than average. But it could have been so much more.
Update 5/19: And now I finally realize I may have missed something critical: the final commercial for Coke may have told us that Don goes back to work with a new idea. Maybe his final smile was actually inspiration for a new ad campaign. That fits what we know much better, and works as a "resolution" (i.e. it doesn't actually resolve his inner demons, but it keeps the show consistent and shows his ability to rise to ever-greater challenges). Good. Now I feel better.