Nightmare Alley is a riveting and darkly evocative film noir from the golden age of cinema. The film, which was released in 1947, stars the dashing Tyrone Power along with the versatile Joan Blondell and is directed by Edmund Goulding, known for his deft explorations of complex characters and emotions.

In the heart of this haunting narrative is the enigmatic protagonist Stanton "Stan" Carlisle, played by Power, who manages to encapsulate both the charisma and raw ambition characteristic of the flawed anti-heroes present in the celebrated noir genre. An ambitious young man, Stan quickly adopts the rhythm of the carnival atmosphere he finds himself in, honing his skills as both an illusionist and manipulator of people. Over the course of the film, audiences follow Stan into a world of unforgiving ambition and obsession.

Joan Blondell plays Zeena Krumbein, a seasoned performer who, along with her alcoholic husband Pete (Ian Keith), introduces Stan to the act of mentalism that she once performed herself. Zeena is an intriguing character; her toughness conceals a profoundly complex past and a lifetime of hard-earned wisdom which she imparts to the eager Stan. In a way, Zeena serves as both guide and warning to Stan, her character allows us to explore the inherent dangers and seductiveness of the carnival world.

As an essential addition to the film noir genre, Nightmare Alley incorporates a fair share of seedy underbellies, moral grays and the habitual pursuit of a nebulous 'big break' that perpetually seems just outside the grasp. However, the film also introduces an interesting blend of themes particularly through its exploration of the occult and the carnival setting, leading to a unique fusion of noir-detective and horror.

Nightmare Alley relies significantly on the captivating performance of Power, who was primarily known for his matinee-idol roles before this. His portrayal of Stan as the complex, charming yet deeply troubled drifter was a bold departure from his previous roles, demonstrating a broader range to his abilities. Power's intense performance, complemented by Blondell's compelling portrayal of the mysterious Zeena, forms the backbone of this film.

Director Edmund Goulding weaves the story masterfully, using a combination of atmospheric cinematography, strategic lighting, and innovative storytelling techniques to bring out the intrinsic duality of his characters and the world they inhabit. The carnival—brightly lit and brimming with life—juxtaposed with the dark and grimy innards of the 'geek' show and the private lives of its employees serves as a visual representation of the dichotomous moral landscape of the film and its characters.

Screenwriter Jules Furthman, whose other works include classics like 'The Big Sleep' and 'To Have and Have Not', adapted the film from William Lindsay Gresham's novel of the same name. With his screenplay, Furthman does justice to Gresham's original narrative, embedding the tale with tension, drama, and an eerie depth that consistently keeps the audiences on their toes.

Fight scenes, carnivals, and an oppressive atmosphere amped up by a haunting soundtrack (courtesy of Cyril J. Mockridge) are other noticeable elements that elevate Nightmare Alley's cinema value. However, at its core, the film remains a psychological exploration of its central character—Stan—and the world he chooses to navigate, coming out as a riveting commentary on human flaw, fate, and ambition.

To sum up, Nightmare Alley is less of a film and more of an intense, psychological experience, one that explores moral ambiguity, the mystique of the carnival world, and the chilling extremes of ambition. A testament to Tyrone Power's acting prowess, it endures as a classic example of film noir, distinguished by its evocative, noir-esque visuals and penetrating insight into the human psyche. Its haunting narrative powered by strong performances makes it a treat for noir aficionados and general film buffs alike.