Re: Why Mark Ruffalo?
Ruffalo was an extremely good Banner, he pulled off the role in a way that I don't think Ed Norton could have hoped to. Saying Ruffalo looked uninterested in the character is simply a misunderstanding of the nature of his performance. In the first film Bruce learned he was cursed with being the Hulk forever and that he had no way out, even by killing himself. He's someone who's frustrated at the world and all of it's aspects but can't die or do anything to fix it. Rather than brooding and being depressed he's simply learned to view everything as a joke.
"I'm always angry" sums it all up, he's always pissed off and frustrated with his life, but he's learned to live with it and find humor his world. Rather than being a boiling pot, he simply learns to let out his frustrations in a peaceful way, having control over his anger. However, he is always frustrated and understands the gravity of his life and can at any time let that anger out as the Hulk.
This to me is the peak Bruce's character can grow, and is part of why the Hulk isn't getting another stand alone film (Why Thor is, when I also think he's reached his peak growth and a movie about Hank Pym or Black Panther would be more desirable however, comes down to money). I liked Norton's performance and have a hard time relating it to Ruffalo's, but of the two the latter is superior in my eyes and those of the general public.