^Which is what makes it so impressive to me that Marvel was willing to trust Joss Whedon with The Avengers, the keystone of their entire movie universe, even though he only has one less-than-successful feature film to his credit as a director. It shows that they looked past the raw numbers and focused on creativity and substance instead.
I think he was the perfect choice to direct. 1. He knows how to create a strong ensemble of well written characters. 2. He has a lot of cred with the base audience.
Also: because he's not a huge director, he comes cheaper. Something Moneybags Marvel likes.