The most important part of any story is your characters. If readers don't like them, they're not apt to keep reading. Even your bad guys, especially in noir need something that a reader can relate to in order to spend time with them. Over at Writer Unboxed David Corbett has an excellent post called "Avoiding Boring Character Biographies". And from Michael Bracken there's a link to Opinionator and an essay by Silas House called "Tell Us Their Secrets".
Some days the links come with themes :)