It doesn’t have the power of the original film. While I have a huge love and appreciation for the talent that went into this adaptation, I just think the story is simply too intimate for a stage musical. The Apartment was emotionally resonant not only because of the dialogue and story, but also because of the nuances conveyed in the acting.
Turning all that subtext into songs for the Broadway stage makes it harder to relate to any of the characters. In the film, Chuck Baxter is so easy to root for BECAUSE he can’t say everything that’s on his mind, and because Fran has her own goals and desires that differ from his own. In the musical, we hear him vent to the audience or sing out his feelings, and we also see his fantasies about Fran falling in love with him.
Despite all of these shortcomings, given the limitations of musical theatre conventions, I think this excels in every other way as an adaptation.