I have seen the film, and it deserves the R rating which is hard to get in Alberta. This is not like Saw, this movie is R for a reason. As you can read below.
Sin City is the most exact adaptation of a comic book ever put on film.
Sin City has more severed heads, dismemberments and acts of cannibalism than The Silence of the Lambs and Freddy Vs. Jason put together.
Sin City, an exquisitely made, unbearably faddish movie that will strike joy into the hearts of all who revere amputation and apocalypse, opens with a swoony love scene culminating in a murder for the heck of it. From there it moves smartly to the promise of child molestation and, with the culprit having had both his face and his balls shot off by Bruce Willis, steams merrily along toward cannibalism, electrocution and the mounting of severed female heads on walls.........
http://www.laweekly.com/ink/05/19/film-taylor.php