I had been considering it after the penultimate show of this season. That really seemed like the wrap up show. ALL the subplots were packaged and tied. The main theme of the past catching up with the present and moving toward the future was finalized when the Past, Present and Future of the abbey hugged on the cricket field. We knew the all important heir issue was taken care of because the one medical obstacle (whatever it was) had been nipped and tucked and the ground was now assured to be fertile. Every episode had aptly captured the moments and flavors as history unfolded and washed over the characters. So what else was there to tell really? What made the story special was done and if it continued it was in danger of becoming just another soap opera. To me the "final" episode was a harbinger of exactly this. It seemed like weak filler where the characters just did stuff without the benefit of any larger purpose. And then of course the ham handed car crash. wtw.
The death of Sybil, while horrifying in it's sudden finality, served the purpose of demonstrating that even the privileged of the time, with access to the best of everything, were helpless in the face of the most basic tragedies. It was upsetting but it gave a 2nd tier character the chance to leave while expanding the main story. The story did not lose with Sybil's leaving but her husband and baby became more significant parts in the larger tail. If it was precipitated by the wishes of the actress than huzzahs to the writers for using the opportunity to expand the story and to do it boldly.
Matthew's death was just stupid. It made no new points, added nothing to the story and did not play off any of themes that compared their current day to ours. My first thought was that the writers felt the story was finished as well, but were being forced to continue in order to feed the money machine it had become. This was their act of defiance.
As far as I am concerned Matthew was a central character to the plot that made Downton special. Without his character it really does just become another soap opera. Based on the method of his demise and the general feel of the last episode, I predict that new situations will become more obvious and sensational while less illuminating and powerful. Before the end I predict increasing amounts of bare skin and possibly vampires.
So I think I will leave it at the "next to last" episode and remember the series fondly.