Threads like this make me feel bad for new devs. Imagine being new and inexperienced, working on a VN for months, posting it here and offering it for free, only to be shredded to pieces by people who don't know how to offer criticism, some of whom didn't even play the game.
Anyway, as someone who would love to play a VN that utilizes the Sin City aesthetic, my piece of advice for the dev is: make clever and limited usage of light sources. Just like all the film noir movies that Frank Miller drew inspiration from, Sin City's scenes take place mostly during nighttime, and there are dominant, hard shadows on almost every frame. You will have to try to mimic that aesthetic while working on your renders. Just turning a regular render with ambient lighting into grayscale and coloring the eyes back in, is not good enough.
Anyway, as someone who would love to play a VN that utilizes the Sin City aesthetic, my piece of advice for the dev is: make clever and limited usage of light sources. Just like all the film noir movies that Frank Miller drew inspiration from, Sin City's scenes take place mostly during nighttime, and there are dominant, hard shadows on almost every frame. You will have to try to mimic that aesthetic while working on your renders. Just turning a regular render with ambient lighting into grayscale and coloring the eyes back in, is not good enough.