One might think that a low budget film adaptation of a Shakespearean play seems an odd choice for one of the most successful modern directors, who can pretty much have his pick of projects. It turns out, however, that Whedon is a big fan of the Bard and would frequently invite friends over to his house to read plays aloud. Then, while on vacation after filming The Avengers, he called up a bunch of actors he knew and asked them to come over to his place and act in Much Ado. The entire movie was filmed at his house in twelve days, and the cast is almost entirely made up of actors who worked on other Whedon projects: Avengers, Angel, and Firefly, to name a few.
One thing that I will give Whedon's version points on over Branagh's is in the casting of a couple of the characters. Whedon's Don John is played by Sean Maher, who is serviceable if not outstanding in the role. In Branagh's version, Don John is played by a miscast Keanu Reeves, whose one expression through the entire movie is a dark scowl. A person would only have to look at him to know that he is responsible for any villainy afoot- and that he probably spends his spare time kicking puppies. His performance of Shakespeare's deathless prose isn't anything to write home about, either.