Okay, so Jarvis isn't the loveable portly butler we know and love from the Iron Man comics. I made my peace with that since it didn't affect the core of the story or the characters (even as an AI, Jarvis was still Jarvis). But on the opposite end of the spectrum we've seen travesties like Fox turning Dark Phoenix into a multiple personality disorder in X3, or Joel Schumaker deciding Bane should be a ‘roided out thug rather than the truly formidable opponent he was in the source material.
So, how far is too far? I, for one, don't mind when filmmakers make minor tweaks to characters' appearance or background, as long as it doesn't affect the "essence" of the character. I think that what happened with Bane was among the worst offenses, while the changes made to Jarvis were essentially harmless.
Let's take a look at a few more examples and see if we can establish a pattern:
Batman Begins: Ra’s al Ghul was never Bruce Wayne’s mentor or trainer, and in my recollection he also used the Lazarus Pit(s) which essentially made him immortal. The original character of Ra’s, as is the case with many characters in the DC Universe, simply would not have fit into the gritty realism Nolan was creating in Batman Begins. Everything else in the film had a pretty solid base in reality, and adding an element like the Lazarus Pit would have bordered on science fiction and would not have meshed well with the rest of the film. Now, I wasn’t exactly on the edge of my seat waiting to see the Lazarus pit, or anything else al Ghul related, so it didn’t ruin the movie experience for me, but I have spoken to a few hardcore Batman readers who were disappointed in the portrayal of the character, although not the movie as a whole. But all in all, Ra’s was still the balance-seeking nutjob who believed a few million lives was a small price to pay to achieve his vision of world order. Check.
X-Men 1: Bryan Singer admittedly had no interest in sticking to the source material. In interviews he has even stated that he wasn't a fan of the X-Men comic books. This, along with the sheer volume of creative liberties he took, makes it hard to figure out where to start. I'll try to leave him alone on the film as a whole, which I thought was fairly well-done (all things considered), and focus more on the character development:
First off, establishing the Jean-Logan-Scott triangle is a must in any X-Men story, and I'm inclined to say that was successful. Check.
Wolverine: Too tall? Maybe. But he was a badass with adamantium claws, a healing factor, and a shady past. Check.
Jean: Telepath/Telekinetic in love with Scott but has hot pants for Logan. Check.
Cyclops: Optic blast, devoted to the team, hates Logan. A lot left out, but no major changes either. Check. Ish.
Storm: Terribly done in my opinion. No hints at an African accent, no hints at being raised as a Goddess, her powers were watered down... All, in all, they made up a new character for Halle Berry and even the character they made up was pretty boring. Anyone who grew up loving Ororo was pulling their hair out in the theater. Bad Singer, bad!
Rogue: Powers, half-check. Dark past, no check. Everything else, epic fail. While she may have played a small part in the movie, what I think the filmmakers failed to realize was that this is someone's favorite character, yet they rewrote her to serve as a plot device.
I think that about sums it up, actually. Every character is SOMEONE's favorite, and no matter how small the part they play within the plot of a film, there are fans out there who will be screaming bloody murder if their hero isn't done some justice on the silver screen.
Granted, there are varying opinions on "doing a character justice." Ask many moviegoers how they felt about the changes mentioned above, and you may get responses varying from a puzzled “What are you talking about, nerd?” to downright outrage that every detail wasn’t carbon copied onto celluloid. I think a good rule of thumb might be to have a “fanboy consultant” on any given character in a comic book movie project. You don’t have to listen to him, I guess, but it wouldn’t hurt to consult with a fan of the character during the production process. Jon Favreu is an admitted Marvel fanboy, and I think we need look no further than Fav’s rendition of Iron Man for an excellent example of how a comic can be brought to the big screen brilliantly.