watched all of them, except for the last season. Enjoyed them very much although when I went back to Upstairs, Downstairs I found that the camera work was so crude compared to today, that I did not enjoy it the way I first did on the small screen in the seventies.
You should catch up on the last season since a movie is now being planned.
I was disappointed in the last season’s episodes. They moved the plot along so quickly it gave you whiplash. But love the s-l-o-w twist and turns throughout the earlier seasons.