The Defenders campaign is still a delight. When we started this, I was worried about a couple of possibilities (I mean, apart from the usual things GMs worry about) because it was a campaign based on a TV show.
One was that the players would ignore the established details of the characters they were playing and just sort of make it a generic super-hero game.
The other was that they'd go to the opposite extreme and slavishly limit themselves to the actions they'd seen, never expanding on their characters, making the resulting story little more than an endless rerun, no matter what scenarios I threw at them.
I've been lucky to get players who haven't fallen into either pit. What I'm seeing (and yeah, often enough I do feel like a spectator instead of a narrator) is a group of characters that are clearly rooted in the established history, but are evolving in creative ways as they go, coming to life in ways I could never have predicted.