Patricia Highsmith sure loved the metaphor of closeted homosexuality as homicidal sociopathy. I found the homoerotic subtext of the Ripley character to be a more effective version of what she does here, but Hitchcock here is as tight and gleeful as he ever was.
Extraordinary concept and adaptation of a well thought-out novel about two men who meet on a train and one of them encourages the other to "swap" murders, "I kill your wife if you kill my father". Filled with Hitchcock's notable dark humor, a memorable ending and the usual visual finesse that one expect from the master director, but it is Robert Walker's psychopath that leave a lasting impression.
The carousel set piece had my jaw on the floor - I can't imagine how absolutely thrilling that would've been in 1951. Hitch does a fantastic job as always, but the suspense he got out that hurried tennis match in the latter half of the film was especially sensational.
Rarely has the influence of German expressionism been mainlined so directly into noir. One of Hitchcock's absolute best, and like all his best, the complexity is not just in the plot or central narrative tension, but in the whole uncanny atmosphere of the movie - that synthesis of all its aesthetic aspects - whose blend of macabre liberation and unspeakable terror makes the theme park an obvious central location.