Keira Knightley plays a very similar role to the one she played in Pride and Prejudice, a feisty, modern woman trapped in a male dominated society. However, whereas Lizzie Bennett's heart and character inspires affection, the Duchess of Devonshire's fosters only reproach and punishment from her traditional and patriarchal husband. Her performance is a standout and demonstrates why she is so highly rated in the face of many disappointing roles in other films. She brings both strength and weakness to the character. Able to deliver withering put downs at her husband and others, whilst showing the pain of her loveless marriage etched into her face.
If Knightley is the lynchpin of the piece then it is Ralph Fiennes that elevates it above a crowded genre. Resisting the temptation to play his character as evil, instead he simply plays him as a man of his times. In Fiennes' hands the Duke feels no need to win any bouts of verbal jousting with his wife as he is secure in the knowledge that, as a husband, he is in complete control of the relationship. The Duke also clearly sees very little wrong in his treatment of his wife and acts, as he sees it, in a logic manner making the whole film feel more believable and, as a result, tragic.
In terms of the cast the only misstep is Dominic Cooper as Charles Grey, who lends the wide eyes of a political dreamer but doesn't have convincing chemistry with Knightley and plays one of the more one dimensional characters in the piece. However Hayley Atwell impresses by playing her character so well it is possible to describe her as scheming, and manipulative as well as sympathetic and loyal without it seeming a contradiction.
The film is deliberately paced so as to give characters and events time to breathe, encouraging the mood that the marriage is a car crash in slow motion, inextricably drawing all the characters further into the muddled mess of their relationships. Overall it's a fully recommended slice of real life costume drama that draws a multi layered drama full of compellingly deep characters from what could easily have been a one note story.