If you like Sin City by Frank Miller, you'll love the Criminal series by Ed Brubaker and Sean Philips.
It's just as harsh, just as dark in style of art and feel.
How is it different? How is it its own creature?
Each graphic novel is called something different and deals with a different set of people, but all inter-linked, with casual comments in one being a revelation when read by anyone who's read the others.
It's also less exaggerated in action and violence, but rather than lacking punch, it has its own nasty, gritty style, using human wekaness and relationships to cause the pain and doubt.
Well worth a look. Preferable as always to start from the beginning, despite each graphic novel being quite easily read independently. The series is still early on, so get into it before the masses!