User control. Interaction. A feast for the eyes.
I find movies way too passive. You simply sit and allow the movie to take you from A to B. With a graphic novel, you can flick the pages in your own time and you can go back and forth as much as you like. Maybe you notice something later on in the story that you recognise from a few chapters back? No problem! Flick back and search for it!
Graphic novels have, just like art in general, an instant impact the moment you turn the page. While with a book you have to read the page to get a sense of what's going on, with a graphic novel, you have the first impression right there, and then you can lean in to get the details as well.
It's an art to lead the eye of the viewer. You'll notice how with well-crafted graphic novels, your eye just seems to effortlessly follow the story, in comparison to badly done layouts where you're not exactly sure where to look and how to start.
(err, I've started rambling! Sorry!)
In summary! Graphic novels are WIN.
And I don't have a favourite genre. I tend to be drawn towards strong character development and beautifully drawn/painted pages (Be it fantasy, sci-fi, modern etc). This makes me very VERY picky, so if I'm not grabbed by the first 3 pages or something, I won't bother.