3. The Hulk Is Counter-Constructive
This point really exists to sum up most of what I've mentioned before, but I'm going to clarify it again based around what Joss Whedon said about the Hulk being something akin to a werewolf. Here's what the
Avengers writer/director actually said when he was asked about how a standalone Hulk flick might fare:
"Is he a monster? Is he a hero? Are you going to root for a protagonist who spends all his time trying to stop the reason you came to the movie from happening? Because the problem is its a very popular character, but its not a superhero. Half of its a superhero, half of its a werewolf. And you cant structure it like a superhero movie, you cant light it like a superhero movie. How do you develop that? It would be extremely difficult."
Whedon's main point stems from the fact that the Hulk is, for the most part, counter-constructive. When he transforms, he creates problems that are separate from those of his alter-ego, Bruce Banner. When the Hulk goes back to being Banner, Banner then has to deal with the aftermath of his actions - actions that he ultimately had no control over. All that makes it incredibly tough to build a working narrative of any kind.