The plot may be hackneyed (see previous review), but the performances ring true, and Leslie Caron is nothing less than sterling. Also, the dialogue in the script (written by veterans Sherwood and Behrman) holds up after these many years and sits better on my ears than many a television or even movie script today.
"Gaby" reminds me of the film Caron did later about the effects of war on ordinary people in London, "The L-shaped Room (1962)," in which she appears more sophisticated, also falling in love with an Englishman, but in which there is no committment on his part and no "happy ending." As the American serviceman, Kerr is a bit stiff in the beginning of this movie, but eventually grows into his role, and Caron is supple as a dancer in her timing and delivery, her English impeccably musical and her face still retaining the innocence and bit of "baby fat" that we cherish in her "American in Paris" debut. Because she had such thorough ballet training, people tend to remember her in the many musicals with ballet routines, but Caron was equally good, possibly even better, in pure drama, such as these two films. Of course, the director should be given credit for drawing out the genuine emotion in her performances, but she could also do comedy, with that great timing that she had (see her in "Last of the Blonde Bombshells" which she did at age seventy with Judi Dench.)
Caron has an authenticity and committment in her roles that comes across on screen for me the same way Audrey Hepburn does, and did from the very beginning, in her "Roman Holiday" debut. Not only were Caron and Hepburn real persons with inner lives (who not so incidentally had witnessed and survived WW II) when they were tapped by and discovered for the movies, they also didn't go through the technical hoops of acting training that the professionals of today bring to similar roles. Actresses of today tend to bring more training and "acting talent" to their roles, but less inner complexity, resulting in, for me, a less authentic performance, regardless of the high budget and publicity hoopla.
Supporting roles by Taina Elg, Cedric Hardwicke and Margallo Gillmore also do not let the movie down. Taina is better in "Gaby" than in the frivolous but enjoyable "Les Girls." And Hardwicke had such a distinguished career that one cannot imagine him consenting to play this very minor part if he didn't think the whole project worthwhile. In sum, highly recommended and requiring hankies for the vulnerable.