Havent read the comic (ordered it from Amazon a couple of years ago but cancelled it due to being short of money at the time - new order awaiting delivery...) But I took the time to read a precis of the story on Wikipedia before I went.
I found the background of Doctor Manhattan and Rorschach troubling, and the violence was quite intense. Especially the scene with the pool table...
I thought it was a f**king good film, but as one review I've read stated "It leaves bombs going off in your head for days afterwards"