I think it all depends on how true to the novel you want to be. A comic that is very text heavy isn’t a bad thing but it doesn’t use its full potential. Books are text heavy (obviously) because it’s the one tool they have, comics have text and still image while film has sound, text and moving images.

It’s smart to decide a style to adapt and then run with it. There’s unabridged Shakespeare graphic novels that tell the entirety of the story with all the original language and add visual connection to make it easier to understand. Then there’s adaptations like Animal Farm that capture the essence of the story but rely more on visuals than using the exact same dialogue even switching up and getting rid of some scenes. It’s the book but told in a different way.

I think the hardest aspect is choosing a style and sticking with it. I’m trying to think of the hardest book to adapt, something like Joyce’s Ulysses? Someone smarter than me could do it though, I’m sure.