A proper well made comic/graphic novel is imho more "grown up" than watching a movie (or even reading a book).
Like a movie, the story is laid out for you in sequence, but unlike a movie you fill in the gaps between the frames with you own imagination. And unlike a book you use imagination to fill in all the bits you dont read.
For example, consider two frames of comic:
Frame 1: picture of a woman beaten to a pulp, a dark figure with his knife raised.
Frame 2: Outside in the dark streets, a caption reading "Aarrggh" is shown
Simple enough. But did the woman die? Did someone come in and kill the murderer? How exactly did the death take place? You're filling in the blanks and conducting the murder in your own mind.
In films/books it's normally show/described to you in graphic detail.
So if you think about it, a good comic (and i dont mean beano/dandy/viz) is like watching a film which isnt handed to you 100% on a plate.
If it wasnt for great comic books then great films like "sin city" and "300" wouldnt even exist. One of the reason "sin city" was so great was it was almost frame to frame replica of the 3 comic books stories it was telling.