The title refers to the protagonist, Harlan Brown, a disgraced LAPD officer turned private detective. Brown was spiritually awakened by and continues to thrive on classical music, hence the title's reference to requiem.
The story was a little dense. If I had taken more than a week between readings, I probably would not have remembered who certain characters were or how they related to the story.
Generally, the book was about a private investigator who is hired by a golf caddy to investigate his long-lost sister and her benefactor. The caddy is a hateful scumbag, and Brown's investigation quickly turns against his client.
This is one of those stories where the city in which it takes place becomes another character. Ellroy was clearly in love with the Los Angeles of 1980, and he makes the city's seedy side come to life. He takes special care in exploring the city's golf courses, which are completely unhknown to non-golfing angelenos.
This book doesn't get into the courtroom at all, so I don't have much to say about its realism. But overall, it was a decent mystery that left me a little empty at the end.