I agree. A lot of the storylines felt rushed and perfunctory. We somehow went from Roger being thrown out of bed in one scene, to him announcing they were getting married in the next one he appeared in.
The Peggy/Stan revelation about their love for one another actually worked for me. They were like best friends who finally own up to their deeper feelings for one another. But such a big moment certainly merited more development. Instead, we just see him looking over her shoulder as she was typing something.
Joan's closing story arc got the best development out of all of them I thought.
Don's big revelation also worked for me. As I read it, Don "found himself" (beyond his Dick Whitman/Don Draper personnas) at the New Age-y retreat by getting in touch with and releasing some of his pain of feeling abandoned and unloved as a child that he carried with him into adulthood. Because he was always disconnected from his feelings, in order to avoid that pain, he had trouble connecting with anyone on a deeper level to create a lasting relationship (just like he was doing when he first arrived at the retreat). He was a stranger to his kids, his wives, his girlfriends, his co-workers, and more importantly, himself; and like a milk bottle sitting on the shelf in the frige, he felt like someone who people liked having around, but not necessarily something they wanted or loved as much as say a bottle of coke or a beer. I guess I've been in enough situations like at that retreat to understand how two complete strangers can form an immediate bond over the disclosure of such intensely emotional experiences.
I wasn't sure if Don had created the Coke ad at the end, but upon further reflection, I think it makes the most sense that he did. After his experience at the retreat, he is in a better position to create an ad about a feeling, which is something he always endeavored to do, but now with feeling. The ending did seem a bit abrupt however.