On balance, Joss Whedon doesn't regret his Avengers experience. He was successful long before taking on the franchise, but it still catapulted him from a TV producer with some wins and some losses into the exclusive club of billion-dollar directors. Moreover, he's a fan from way back and the chance to speak for his childhood heroes called him into action not once but twice.
But this greater level of success brought some frustrations with it. Pretty much every report on Whedon before, during, and after the movie's release has stressed how exhausted he is. Though he has pondered doing more creative consultancy with Marvel and maybe even contributing a script for Avengers 3, he's very clear on one point: Avengers 2 is his last Marvel movie as a director. Making Avengers 3 "would be four years of my life," he says, "after which I would be twenty years older."
Creative types know it well: no matter how much we put into the work, there's always something wrong that jumps out at us when it's done. And when you're making movies with a studio that has certain demands about how things need to go, sometimes that wrong thing is actually somebody else's idea. Or sometimes the thing will feel like the worst problem in the world during the creative process and turn out to be for the best. Spoilers for both movies to follow.