The first thing about this series is that the photography and production design is sumptuous and stunning. Even if the story and characters were of no interest, the visual appeal of this is memorable.
The only strange thing in this aspect of the production is that the music in scenes for the parties is jazz - 1920s sounding jazz. It is very odd and historically inaccurate for the social status of the story as jazz entered England in 1919, apparently.
As to the core of it, well, it is an abbreviated working of a complex set of novels written in a certain way and Stoppard has done well with the time limits etc of the medium. It works but one is always aware of what is being abridged to make it fit.
Cumberbatch is the most intense, internal English leading man in a long while and seems to have borrowed Jeremy Irons's mandible crunching pensiveness. But he is absolutely right here.
Hall as Sylvia Tietjens is ravishing and confused in right order. Her performance is entitled' and arrogant, though it might be a bit too modern in its overtness.