I'm here to add my voice to the chorus praising the new movie Love and Friendship. Jane Austen's epistolary novella Lady Susan is actually rather sketchy, though it does have a few choice lines most of which make it into the movie. But the dialogue and characterization here are mostly the work of writer-director Whit Stillman. I'd only seen one of his movies before, and I didn't like it, but this is an Austen pastiche for the ages.
The acting as much as the writing makes it so. Kate Beckinsale is ideal as Lady Susan. Those little asides she makes in her conversation are tossed off with perfection. This is a performance to match her epochal turn as Flora Poste in Cold Comfort Farm twenty years ago: equally manipulative characters but otherwise entirely different.
In Cold Comfort, the fatuous twit was Mr. Mybug, played unmatchably by Stephen Fry. He'd accordingly have been ideal for Sir James Martin here, except that he's now too old for the part. He does appear, in a very small role, and Sir James instead is played by Tom Bennett, a British TV actor unfamiliar to me. Unlike Mr. Mybug, Sir James is an amiable gentleman, but he's also mesmerizingly dim-witted. Bennett develops a perfect air of Sir James not having the slightest idea of what he's going to say until it comes out of his mouth. My favorite bit is his reverie, having being told that there aren't twelve commandments but only ten, on which two we should therefore discard. I've read that Stillman added this in a fit of inspiration and handed it to Bennett just before filming; you couldn't tell.
The movie dumps a huge load of characters, some of whom aren't very important, on you at the beginning, so the unfamiliar may need some time to sort things out. It'd probably be best if you read Lady Susan first. There will still be some surprises in the plot. And pay attention throughout, as some of the more important events happen offstage.
Only flaw I noticed: some anachronisms in the greetings and introductions. You wouldn't quietly greet someone by saying "Hello" at this date. And "Mrs. Catherine Vernon" is an incorrect form of address for this character.