Sin City 2: A Dame to Kill For has a striking visual style, an engaging plot, and fun characters and cameos.
I liked the first Sin City, although I haven't read any of the comics. I didn't remember much about it, so I read the Wikipedia article on it before watching this one. I didn't think it really helped; it was just a jumble of names - X did this, then Y did that, and I couldn't even keep the names straight while I was reading it. I think it actually was useful, though.
I love the visual style of the sequel. I wanted to see it at the theater, but it looks like it's not coming to the cheap one. It's amazing how much it looks like you're watching a live comic, and all the highlights and color pops were great. I liked the noir-style narration.