Pretty great (spoilers)
We watched every episode as they came out, from the beginning, and thought this was a great addition.
The Lady Mary character was so great in this one. Really handles that assassin.
Carson was very funny, maybe more so than anyone else.
Mr. Bates didn't seem to have much to do, and surprising that Mary's husband is there so little.
From the end gathered that Maggie Smith is ready to hang it up and they wanted to have a passing the torch scene. Perhaps her illness or death will be the raison d'être for the next movie installment. Then Mary can inherit her cutting dialog.