Film-Noir
I was getting this familiar feeling while watching the movie.
This is Film-Noir version of Batman - not pure but atleast a treatment/touch/cross-over whatever you like to call.
A protagonist who is not out and out a hero; major and the last part of the puzzle was solved by catwoman and not batman
Closed environment, frequently visiting a particular central point - The Club in this case
Twisted plot with several persons entangled by their actions and all the dots getting connected only at the end.
Night life, Corrupt cops, Cars, Hookers - all movie has it but this had it with that typical Noiresque style.
And ofcourse that typical Cinematography
Simplicity, no fancy gadgets, guns. A classic Batmobile;
you blend The Maltese Falcon, 1966's Adam West Batman TV Series and The Dark Knight, you get this.