Westlake's strengths include a talent for intricate plots, apt bits of metaphoric description, and precise and concise characterization. Even this early in his career, all those strengths are present in The Cutie: you don't need to read this just to be a Westlake completist. You don't even need to care who Westlake is, though you will by the end.
Standalone novels like this one put Westlake firmly in the line of James M. Cain and Jim Thompson. The Cutie's first-person narrator, a troubleshooter (pretty much literally) for a mob boss in New York, impresses the reader with his determination to find a killer even as his own almost split personality when it comes to violence becomes more and more apparent. He's not a dead soul, but he's probably damned.
Nonetheless, the narrator's pursuit of a murderer who's made things hot for his mob boss hums with menace and moral rot. And the narrator grows just enough in his own self-assessment that the ending comes as a grim epiphany: the things that the narrator assumed worked one way may instead work completely differently, at least when you're the boss.
Verisimilitude makes this sort of street-level thriller work. I don't know how accurate Westlake's depictions of the working of crime in 1960 really are, but they seem real. One of the best bits is a classification of all cops into one of four categories, with the pros and cons of each type. It seems like the sort of thing a killer who's always been too evolved for his econiche might formulate during his downtime. And it's moments like that, among others, that make Westlake worth reading decades after what were supposed to be disposable novels were published. Recommended.