Frank Turtletaub’s review published on Letterboxd:
This film was incredibly ahead of its time, in least in terms of content. Latent sexual tension is seething through the celluloid through the first act, changing the game the film a risque veneer. It makes sense that a year in film that also featured Psycho and Breathless also had something as subversive content wise as The Apartment.
On a plot level The Apartment also succeeds in creating more of a two act strucutre--the first half of light-hearted, raunchy comedy and the second half dramedy that plays into the darkness of the heart. In a really brilliant, Wilder/Diamond's script doesn't go for obvious reveals or cringe-humor inducing ploys of dramatic irony. Every plot development (specifically Baxter's discovery of Kubilek in the bed) gives the film the weight it needs, while maintaining the dramatic ironies in order to pump out humor in a needed fashion.
The ending is very sweet, and it does feel very Hollywood, but it is absolutely earned. You want the best for Baxter due to his kind demeanor, something the film never makes domineering or overbearing. Still, one wonders if this had been made in a different era/country/studio, how could it have gone? Alas, but without the Hays Code and the American market, we never would have gotten this obliquely sensual masterpiece.