@freak_spawn: Wait, so what you're specifically asking is how much directors of COMIC BOOK movies can alter the source material? Because your title and posts didn't communicate that at all.... It took ten posts to decipher this.
I feel the writers and directors of comic book movies should have the choice to alter the characters and motivations as they see fit. But they should always weigh the risks in doing so. The two Tim Burton Batman movies are very different from the accepted vision of Batman (Burton's Batman has no problem with killing dudes, a young Joker killed the Waynes) but are entertaining movies.
Then there's The Spirit. I laughed a lot and had fun with The Spirit, but it had NOTHING to do with Will Eisner's cast of characters and tone. Frank Miller just seemed to be pissing on his friend's grave with that one.