It was a good ending. That proposal by Don was sort of out of left field. It'll be interesting to see how that plays out next season.
I think that Don and Peggy have a connection between them that will always linger. They both know things about each other and trust each other. I think Peggy has always wanted recognition by Don, rather than just being another girl for him, and that has lead to attraction for him.
Don, on the other hand, likes that Peggy has sort of earned her worth at the company, but still doesn't respect her as much as he should, or at least until recently. I think he has some sort of attraction to her, but also views her as a daughter type, or even someone to him like Anna was to him.
It was pretty obvious to me that Joan didn't have the abortion. idk if it was just her getting fatter, since she's not that skinny to begin with, or they were purposely showing a baby bump, but either way, pretty obvious.
I hope ty things happen to Betty next season if they show her. I don't know what she expected at the end when Don comes to the house, but it's clear, and has been, that she's not over him. She is a terrible mother, doesn't know what she wants and deserves to be alone. The difference between her and Don is that she had everything she ever wanted growing up, it seems, and is just a spoiled brat that can never be satisfied and is still a horrible person.
Don is no saint, but at least he's inherently a good person. His mom was a pros ute, and he watched his Dad live dirt poor, and die from a kick to the face from a horse. Add to that that the people that took care of him after that hated him, and that's why Don has the commitment issues and problems that he has. Not to mention he's not even who he says he is.
Also, I don't know how January Jones hasn't won a best actress Emmy yet, because I'm not ever sure I've hated a character so much after initially liking her. Doubt she'll win one for season 4 though since she wasn't in about half of the season.
Hopefully, Hamm wins an Emmy for season 4. He arguably could have won one instead of Cranston winning it for the last three years.