The main problem with the Hulk, visually, is that it's so difficult to render an out of control beast that still fits in some kind of reality in the present day. When the Hulk emerged as a comic book character and tv show, bodybuilders were just big enough to look a little freaky and a real actor could take on the role and not look out of place. Now, with all the chemicals available, pro bodybuilders look downright otherworldly - taking the Hulk a step beyond that makes him cartoonish. In the first film, he looked like the Pillsbury Doughboy; in the current offering, Hulk looks like a malformed children's action figure plopped down on a city street.
The solution would be to visually remake the world that the Hulk lives in to be more like a comic book. Ang Lee experimented a bit of framing devices and transitions that drew on comic books for inspiration in the first film, but I'd take the idea further, creating a visual look that is a kind of "hyperreality", similar to what viewers saw in "The 300". It would bring the films and the character into a new visual realm more based on the comic book origins and content that would probably be less disconcerting to the audience. It would also free the filmmakers to get a little more creative with the storyline and characters - as a kind of hybrid animated film in its own reality, the movie could be funny without being coy and be dark without being too frightening.