What is the difference between Daredevil and Iron Man? Heck, for that matter, why did Tony Stark fly so much higher at the box office than Bruce Banner during the summer of 2008?
Simple. Jon Favreau lets his actors off the leash.
Both Robert Downey Jr. and Edward Norton Jr. were directly responsible for creating the majority of the dialogue in their respective films. The biggest difference? Norton did it with daily re-writes of the screenplay. Downey did it off the cuff. He was allowed to become the character and let it flow.
The spontaneous ad-libs and improvisation that was used for Iron Man was so drastic that Gwyneth Paltrow often had trouble keeping up - she never knew what Tony Stark was going to say next! Robert Downey embraced his inner superhero so completely that he was a fountain of serendipidous perfection.
Fearless prediction: Iron Man 2 will break all the box office records it gets in its sights. This time Favreau's stable of Improv Theater ponies includes Mickey Rourke and Scarlett Johannson. It will be the biggest blockbuster ever, naturally.