Not because it is too violent. Not because I’m sick of comic book movies (although I am). And not because I am broke. But because it has a “special guest director.” I watch an awful lot of movies, and I can’t recall ever seeing the credit “special guest director” before. That said “special guest director” is Quentin Tarantino, a man bested only by Kevin Smith for ruining cinema, is even more reason to run screaming for the hills.
The reason you’ve never seen that credit before is that it’s against Director’s Guild regulations. Rodriguez had to drop out of the Guild because he wanted to give Frank Miller co-directing credit, and that was the only way. I couldnt’ even tell which sequence was QT’s–probably the one with the samurai swords? Whatever. Q and Rodriguez are hacks. So is Kevin Smith. (And the 2005 incarnation of Woody Allen.) The real reason not to see Sin City is that the stories blow:
http://worldfilm.about.com/od/r/fr/sincity.htm