Why Oh Why do screenwriters think they're better?
A book gets made into a movie because people liked the book! And the absolute hallmarks of a Raymond Chandler book are the STORY and the DIALOG. This movie captured neither the fluid intricacy of the book's plot, nor the intelligence and wit of Chandler's detective. I give it a 3 out of 10.
In addition, Marlowe is notoriously difficult to cast because actors in the 40's didn't have the physicality necessary to take on characters from the underworld and still be attractive to women, and actors nowadays would never willingly walk away from the dame--but walking away from the dame is an absolute necessity if one is to be Marlowe. The only actor I can think of that had all of the necessary tools was Mitchum. Maybe Errol Flynn if he had bulked up a bit and had a good director.
Well anyway, I thought this movie stunk.