Chick 2 says:

Hoping for something a little more historical or, in these times, political, or even something as different as Sofia Coppola’s Marie Antoinette, The Duchess was somewhat disappointing.  Based on the true story and adapted from the Amanda Foreman novel Georgiana, the Duchess of Devonshire, the story quickly dissipates into soap opera love stories rather than epic romances. At her first dinner party engagement the Duchess voices her political views and gives hope for a more intelligent and meaningful movie, but just as abruptly as the Duke leaves the table apparently bored with political rhetoric, the script leaves behind depth and underlying story.   Kiera Knightly gives yet another impressive performance, and Dominic Cooper is proving that he could quickly rise to the same ranks.  Ralph Fiennes can always make you love him or hate him and gives another stellar performance as the Duke of Devonshire.  With such extravagant sets, wardrobe, and actors I would have thought that the script, camera work, and continuity would have been better, but good acting goes a long way.  As the love triangles unfold, it just makes a girl thankful not to be married into royalty, especially in the 1700’s.

IF you are looking for yet another period piece about adultery and bearing a male heir with talented actors doing their thing, THEN GO.