Ruffalo is certainly a name, but he's not a big one. I'd venture to say he's an unknown to a lot of mainstream moviegoers who may barely recognize him from "big" movies like Shutter Island or Zodiac. He's a pretty low key actor, perfectly willing to play the second fiddle to flashier actors like Leonardo DiCaprio or Adrien Brody, so I imagine he'll be the team player Marvel is reportedly looking for.
I don't mind the casting -- personally, I wish they'd pretend Ang Lee's Hulk was part of this greater continuity and recast Eric Bana -- but Ruffalo seems like a deliberately neutral pick. He's a good actor, but I've never seen him ... well ... Hulk out. Bana has that Australian unpredictability (and a role like Chopper) to his credit, and Norton is nothing but intense and tormented. But Ruffalo seems like a Bruce Banner who has it all under control. Maybe that's the angle they want, though. Maybe we're going to see a new Banner who has it all together, only to be manipulated into releasing big green monster again.
That's my take, though. What do you think of Ruffalo as Hulk?