As far as I know, I can't put a time signature on the whole thing. Some stories could be a prequel, some could be a sequel. I just checked IMDb FAQ's because I was curious, and it says that none of it is chronological. There's also a mention of Brolin being a pre-surgery Dwight in the FAQ's. I have been a huge fan of the first for years, and I am really excited for this one. I've watched the original on STARZ probably three times in the last month.
When The Spirit was first advertised, I thought that was going to be the rumored sequel to Sin City, but I figured out before seeing it that it wasn't. I liked it a lot, and if you take it for when it was written and the time period it portrays, it is a fun watch. Just don't confuse it for a Sin City movie despite the looks.