Graphic novels are an emerging genre of literature. They supplement a plain story with pictures, and hence stimulates the senses. The visual stimulation arises from pictures that give specific vibes and it engages the mind more than just words. They, in turn, help you stay with the story, make complete sense of it and grasp it more fully.
Visuals aid comprehension faster than words. A picture speaks louder than words, they say.
Besides plain stories, they give the opportunity to stay engaged even for people with learning disabilities like dyslexia and make the reading process more accessible. Since reading of all forms improves critical thinking skills, a more inclusive environment is all the better.