The first reason is that a graphic novel is more suited towards long stories. There can be multiple volumes and so one can take their time with the story and get a lot more detail in while still keeping the reader interested. This way, the whole story can be told and not have to be condensed to under three hours. Paradise Lost is a long epic poem with eleven books. It would be difficult to fit all that into a movie that would keep the audience engaged, but a a series of graphic novels would work really well for the length.
My next reason is that graphic novels work better with elements of a fantastic nature. Paradise Lost has a lot of elements and themes that could be rather bizarre if they were done in a live action movie. The suspension of disbelief would be easier in a graphic novel since we're dealing with art work, or a stylized form of a story. For example, graphic novels would make it easier to see the visual representation of Sin and Death. I feel that whole scene would be just bizarre in movie format, but I could see it in a graphic novel. They can get away with more strange visuals than movies can.
Another reason is that the possibilities for the artwork would be incredible. I've seen a lot of the artwork that people have done for Paradise Lost, and some of it is rather breathtaking. Imagine if someone could create such beautiful artwork, such as this:
and put it into story form. There are also a lot of scenes that have massive amounts of angels and devils, which could become a beautiful picture. Graphic novels not only deal with the story itself but add a whole new level of complexity with the visual aspect. For a book as complex and intriguing as Paradise Lost, adding a visual aspect would give some phenomenal new opportunities to analyze why an artist interpreted that scene in that particular way.
Now there is news that there will be a graphic novel adaptation of the movie adaptation of Paradise Lost. I'm not really excited about that idea because if the movie doesn't capture the theme and greatness of Paradise Lost, than neither will the graphic novel. Also, adaptations of adaptions are rarely very good. I think it would be better to do an adaption directly from the text. What do you guys think? Would a graphic novel form of Paradise Lost work, or would it just detract from the complexities and style of the poem?