Fundamentally, I rather enjoyed the finale episode of Doctor Who; likewise with the penultimate episode. It was not a surprise to see the reappearance of the Master, however - I am disappointed that Peter Capaldi (the 12th Doctor), Pearl Mackie (Bill Potts) and Michelle Gomez (Missy) are leaving/have left the series as I found they attributed well to the series. Regarding Bill, I am pleased that she received a happy ending and it leaves the possibility of her character returning later on, open. Furthermore, it appears that many people disliked Clara Oswald as the previous companion of The Doctor; however, in my opinion - she was excellent at portraying her character and therefore is one of my favourite Doctor Who companions. I feel that Peter Capaldi and Michelle Gomez as well as the writer/s, portrayed a dark and complex atmosphere to the Doctor Who series; which really worked well, indeed.
As for Missy, her wit made her a very amusing character - conversely, although not with the same conscience and morals as the Doctor, she was depicted as less ruthless than the Master and I felt that this was portrayed successfully; in the finale episode of the most recent series.