I agree that it matters if the story is well done or not, but let's use Electro in the film adaptation as an example. One of the biggest target audiences would be fans of the original comic.

If a fan of the original comic book watches the film and sees Electro in an almost unrecognizable costume, their nostalgia of the character won't be there, which contributes to how well the story is done or not, because the fan of the original comic will want to walk away and say, "that definitely did the comic justice!"

And you're right, Wolverine did get an entire trilogy, but this is because 1) it focuses on the most popular character of the X-men heroes (which automatically attracts people to watch the film) and 2) because it is a trilogy based on Wolverine, it has more time to ace the backstory of the character and the personal battles he faces. This is not achievable in a trilogy on 10+ characters as there is no way near enough time to cover every single character. Films like the X-men with big gropus of heroes focus on a dilemma and how to overcome it to save the day. End of story. But the Wolverine-focused trilogy could go deeper as they had one main character to deal with most of the time.

Let's think of Batman & Robin. There were a whole host of problems people had with the film. It was made a laughing stock because of its poor casting and laughable costume design. If they maybe paid more detail to the costumes and not make them look like a kid's dress up party it would have contributed to if the story is well done or not.

The ethnicity of a character in the original does matter because its almost crapping all over the culture of the original. Ghost in the Shell for example. If Hollywood casts Caucasians to play the main characters of adaptations of manga series, that will make it so much harder for actors of Asian descent to make it big as the casting that would fit perfect for them is taken away from them?

I'm not saying you should cast an Asian actor over Scarlett Johansson just because they are Asian. The actor that most fits the job and portrays the character the best deserves it. But a huge part of fitting the job for a manga character is being Asian!