The Avengers: Age of Ultron director - who created Buffy the Vampire Slayer - explained to Entertainment Weekly that he found Kristen Stewart's character to be too "passive" throughout the series.
"A small part of you is like, 'Well, you know, I did that first. I liked that band before they were popular'," he joked. "The thing about Buffy for me is - on a show-by-show basis - are there female characters who are being empowered, who are driving the narrative?"
The filmmaker went on to say: "The Twilight thing and a lot of these franchise attempts coming out, everything rests on what this girl will do, but she's completely passive, or not really knowing what the hell is going on.
"And that's incredibly frustrating to me because a lot of what's taking on the oeuvre of Buffy, is actually a reaction against it. Everything is there - except for the Buffy. A lot of things aimed at the younger kids is just Choosing Boyfriends: The Movie."
Buffy the Vampire Slayer was originally a feature film, and eventually spun off into a hit television series which aired from 1997 to 2003.
Whedon previously promised that the infusion of the titular villain in his own upcoming film Avengers: Age of Ultron will raise the movie's stakes.
Photo Gallery: 'Buffy the Vampire Slayer' - Then and Now