Much Ado About Nothing is a 1993 adaptation of the Shakespeare play directed by and starring Kenneth Branagh. Michael Keaton, Robert Sean Leonard, Keanu Reeves, Emma Thompson, Denzel Washington, and Kate Beckinsale also star. I have the DVD, long languishing in my stack of to-be-watched films, and I'm glad I finally got around to it.
You can read a plot description of the play itself here at the Wikipedia entry, but it's not at all necessary for understanding and enjoyment.
It's well-reviewed, though Keanu Reeves earned a nomination for a Golden Raspberry Award for Worst Supporting Actor. He is the weak link here, but I like him at the worst of times.