Neil Gaiman's Law of Superhero Films:
…the closer the film is to the look and feel of what people like about the comic, the more successful it is (which is something that Warners tends singularly to miss, and Marvel tends singularly to get right)
…Which, I suspect, is why Sin City and 300 worked. They were like having the comics happening up on the screen. The thing that people liked about it was there. With The Spirit, what the reader responded to is Eisner's lightness of touch and mastery of story, his humour and his humanity -- and a world that looks like Eisner drew it. The moment that it's obvious that that isn't there it almost doesn't matter what is there instead. According to Gaiman's Law, the more Sin City looked and felt like what people like about Frank Miller's work on Sin City, the more successful it was going to be with audiences, but the more The Spirit feels like Sin City and not like Will Eisner's The Spirit, the less successful it's going to be.
If the law is true, it seems to suggest that people who do superhero films don't know what they're doing and only by copying their sources faithfully will they have any hope of stumbling upon something good.
I think it suggests that a certain subset of those people who do superhero films don't know what they're doing.
The right way to approach such a project is to say "This is an adaptation of a popular work. What are the essential qualities of the original that made it popular, and how do we translate those to a new medium?" The wrong way is to say "This is a superhero movie. What other superhero movies have been popular lately, and how can we make this movie like those movies?"
If a comic (or really any work) is successful enough to be adapted to film, it must be because there was some quality in the original that made it popular—the story, the characters, the visual style, whatever. If you throw that away, you're just left with an ill-fitting suit you have to stuff your own ideas into.