Wow, this is a tough subject but not as sordid a film as I figured it would be, although be warned the last 30 minutes are really rough in spots. Speaking of spots, this is a bloody movie in spots, too and very profane after the first 40 minutes. Yet, despite the unpleasant nature of the story (making a "snuff film" - filming the killing of people) it's a riveting one, well-acted and doesn't overdo the violence. The characters in here are some of the most despicable you could find - killer and porn kings.
Even our hero here, played by Nicholas Cage, starts off as a clean-cut fairly straight dude, and changes for the worst, too. Joaquin Phoenix has a good line in here, with the prophetic statement, "The devil doesn't change; he changes you."
James Gandolfini and Peter Stormare play characters about as bad you'll ever find in a movie. This film is not, as they say, for all tastes. It will turn off a lot of people but it is interesting and good revenge story, if you like that sort of thing and know what you're in for before watching this.