There are some really cool Fincher moments in this featurette, either through Jake Gyllenhaal or Mark Ruffalo talking about him or original statements by the director. I don't like repeating myself here, but to me Fincher is the ideal director, not only by his choice of theme and stories, his enigmatic camera style and the perfection of his work, but especially by his total dedication to delivering the very best work he and the entire cast and crew are capable of!
I was amazed to learn so many things that were going on in the preprodution stage of this movie, such as that David Fincher insisted on Gyllenhaal playing the lead role or otherwise he wouldn't direct it, and such as not taking Ruffalo's inital "no" for an answer.
So much in there, it's hard to sum it up, and you guys will watch it anyway. But this is a Ruffalo quote about Fincher I really loved: