The movie is the screen adaptation of the book GEORGIANA, THE DUCHESS OF DEVONSHIRE by Amanda Foreman. It follows the life of Georgiana, the Duchess of Devonshire, an 18th century aristocrat who was famous and much loved by the subjects.
The cast includes Keira Knightley (Georgiana), Ralph Fiennes (the Duke), Hayley Atwell, Dominic Cooper and Charlotte Rampling, among the rest. The leads are all English, as is very common in such screen adaptation of novels. The cast has done a good work and you can always expect a movie to be worth a watch if it stars Ralph Fiennes.
According to me, the movie is not very enjoyable or something you could watch alongwith your family, but it is very original and somewhat depressing at times. The story is set in the 18th century so that means you can witness the beautiful countryside scenes, vast gardens, big hats and of course, huge mansions and palaces.
The good part is that the movie has been made with maturity and the crew hasn't tried to glamorize the plot, its original, natural and straight forward, so are the characters of the movie. Once again, Keira Knightley has proved that she can be trusted with roles in period movies.
I think I would recommend this movie to you since I found it honest and mature. Don't watch it with your kids, its not very advisable, otherwise they would bug you with questions that would well embarrass you!