Sunset Boulevard is a classic portrait of behind-the-scenes Hollywood, no doubt because it was made by a director whose roots were in German cinema and whose outsider sensibility was much darker than that of his home-grown colleagues. The combination enabled Wilder, along with with co-writers Charles Brackett and D.M.Marshman Jr., to adopt an observer's perspective on the Dream Factory, embodied by the central character and deceased narrator, Joe Gillis (William Holden), a failing scriptwriter on his druthers who becomes the willing but self-loathing toy boy for a reclusive silent-era film star (Gloria Swanson) living alone in a crumbling mansion with her devoted butler (Erich Von Stroheim). She is unable to accept that her time has passed and is becoming increasingly delusional believing that she is about to make her "return" to the silver screen and public adulation. Although only fifty years old Swanson's Norma Desmond is a faded star descending into madness and the film's final scene captures this brilliantly.
Holden in what was for him a ticket to the big-time after a long career in small roles won a Best Supporting Actor Oscar. Swanson was nominated for an Oscar but did not win (nor for that matter did Bette Davis for the thematically-related All About Eve, the award going to Judy Holliday in Born Yesterday) despite the fact that it is her histrionic performance that brings Wilder's rather too detached approach alive.
The opening scene, which features the iconic image, shot from under water, of the dead narrator face down in a swimming pool is a brilliant piece of staging but in between the main story is padded out with a dutifully handled sub-plot involving Joe's relationship with a young aspiring female scriptwriter (Nancy Olsen) and neatly packaged with Franz Waxman's orchestral score which won Best Score for a Drama.
FYI: The film also won Oscars for Art Direction and Original Story and Screenplay.