God knows I love a costume drama. And, although I thought there were some flaws in the plot, I also enjoyed the first series of Downton Abbey. But now that I am caught up on the second series I must say, I think it's really kind of lame. I won't catalogue the things that made me roll my eyes like I did when I watched the terrible film version of Possession because that film was acres worse than Downton. Besides the often clumsy plotting, blocking, and writing, the thing that most annoys me is that it seems like the writers got out the big bag of WWI-era English costume drama tricks and decided to use a little bit of everything. Even that would be okay if they actually broke some new ground. But they don't.
You can rent a pretty house and dress up a lot of pretty actors but if your script is lame the result will not be quite so pretty.