This isn't a comic book/graphic novel movie. Unlike Snyder's past films, this is completely original. Story is by him and the he co-wrote it as well. Watchmen, 300, Sin City, etc, were all based off graphic novels (I'm pretty sure).
And since when were comic book/graphic novel movies bad? Having seen quite a few of them, they're all really quite good. Iron Man was excellent and I think it's better than The Dark Knight in terms of comic book films. The Dark Knight is still great though, as goes for Batman Begins. Then there's Spiderman (the first one wasn't bad), Spiderman 2 (which was awesome, we just don't talk about the third one), The Incredible Hulk (the Ed Norton one), Hellboy (it kinda bored me but it was still pretty good), X-Men (the first two were pretty good), and some upcoming ones like Thor (although it looks pretty meh), Captain America (which is actually looking pretty decent), and The Avengers (which I'm dying to see).
Anyway, I saw Sucker Punch again yesterday (mainly since some of my friends still didn't see it and they wanted to go see it). Second time around I liked it even more as I knew what I was going into when I entered the theater. I was able to focus more on the plot and still enjoy the action. It's not all that confusing. If you can understand Inception you can understand this. But there's a lot of small details that I missed the first time that were nice to pick up the second time. It's kinda like The Matrix, where you can see it 20 times (like I have, I absolutely love The Matrix) and pick up something new every time.
It'll definitely be a cult classic. A majority of people will hate it but people, such as myself and my friends, will love this movie and defend it to the death. I think it's a good action movie with a surprising amount of complexity and interpretation and is a strong start for Snyder's entry into his own ideas.