Originally Posted by Scar Predator
An adaptation should always make as few changes as possible. When a CBM is being made, it's because of a printed work that already has proven characters and storylines that have worked. Otherwise, the film wouldn't be in production. It's certainly true that some things don't translate well to the silver screen (this is especially true of costumes), but the biggest CBM flops are ones that decided to ignore their source mythos, ie Catwoman.
I agree with Happy Jack - it's a case by case basis. I mean, you've got Blade in your sig as one of your favourite comic book movie adaptations, and that's pretty drastically different from the source material. And I'd agree with you, Blade is a kick ass movie. It's pretty clear that those writing, directing and starring in it have respect for the script - if not the comic book - and to me that's the key component. Changing things isn't necessarily a 'no-no', but you've got to at least respect what you're doing.
I much prefer Singer's X-Men and X2 to the rest of the X-Men related films, and yet they were directed by someone that seemed to look down on comic books. (At the time anyway - not sure if he still does.) Even if the director isn't a fan of the comics, if they have some respect for the characters that are being portrayed in the film then changing certain elements isn't always the kiss of death.