This article by Stanley Crouch on Slate.com is one of the best written and most entertaining surveys of film noir I have read: Noir America: Cynics, sluts, heists, and murder most foul. An extract follows:
Noir’s popularity was inevitable. How could American audiences resist the combative stance of an unimpressed hero whose ethos could be reduced to: “Is that so?” How could they fail to be lured by all of the actresses cast as Venus’ flytraps? Everything in film noir takes place at the bottom, in the sewers of sensibility. It holds that the force of the world is not only indifferent to, but obviously bigger than, the individual, which is why personal satisfaction, whether illegal or immoral, is the solution to the obligatory ride through an unavoidably brittle universe.