Crossdreaming-wise, Goodbye Charlie was a big deal for me, when I first caught it on TV, in the early 1980s. It pressed some, but not all, of my particular buttons (almost before I even knew I had them!) back then; for instance, you never really get much of a good look at the male Charlie to any great extent, nor his interaction with others, since he's shot and falls overboard at the very beginning of the movie... so all the contrast is from comments about what pre-transformation Charlie used to be like. Still, gender-swapping films were pretty rare then, even moreso than today, so you took what you could get. My favorite from those times was (and still is) Dr. Jekyll and Sister Hyde (1971), mainly because it best achieves what it sets out to do, as a movie. But, really, apart from a few TV episodes (or bits from episodes), filmed MtF TG in the USA basically consisted of Turnabout (1940), Goodbye Charlie, Frankenstein Created Woman (1966), Myra Breckinridge (1970), The Christine Jorgensen Story (1970), Dr. Jekyll and Sister Hyde and I Want What I Want (1972)... and half of those weren't normally shown on TV.
Goodbye Charlie is professionally-made, I aesthetically like the era in which it was made, and Debbie Reynolds gives it her all, though I find her to be a bit too hyper and shrill, at times. Tony Curtis is okay, but comes across as a bit stiff and false to me. Though the film is a comic farce, like many early-1960s comedies, it isn't really all that clever or laugh-out-loud funny... and Walter Matthau's character seems to have walked in from a different, cartoonishly-broader comedy. Amazingly, I liked Pat Boone's "playboy" character, who had some potential, but was underutilized (he kind of gets crowded out by Curtis and Matthau). But the film does have its moments, mostly when Charlie emerges from his/her temporary amnesia and realizes what's happened, and a bit later, when some feminine thinking and behavior (stereotypical or not) start seeping into his/her mind. The ending (which I won't spoil) is pretty dopey, however. Still, it's overall better than Switch (1991). The low-budget, softcore unofficial remake, Cleo/Leo (1989), actually does the story better than both of its more-prestigeous rivals, despite its own deep flaws.
Sociology and gender politics aside, let's take a moment to look into a bit of film history and see what potentially might have been...
I did a little detective work (starting at Wikipedia, then verifying sources) on the production of Goodbye Charlie. If it had been filmed a few years earlier (in 1961), as originally intended, it might well have starred Marilyn Monroe as "Charlie" and James Garner in what became Tony Curtis' part, as both actors were offered the roles. Here's how they looked in 1961:
There's no information on who would've directed this version with Marilyn and Garner, though her last film at Fox, Let's Make Love (1960), as well as the Fox film in early production at the time of her death (though she had just been fired from it, due to personal problems), Something's Got to Give (intended for a 1962-1963 release), were both directed by George Cukor (The Women, Gaslight, Adam's Rib, My Fair Lady). As an interesting sidelight, the uncompleted Something's Got to Give was overhauled, retitled Move Over, Darling, and the male lead was played by James Garner (to have been played by Dean Martin in the Marilyn version). The stage play was apparently a somewhat different animal from the film version, though sharing the same overall plot, with a more androgynous Charlie, played on-stage by Lauren Bacall.
Goodbye Charlie was also offered, a bit later, to Billy Wilder to write/direct, but he turned it down, mainly because it was a 20th Century-Fox production (which had bought the rights to the play back in 1959, as a film vehicle for Monroe, before its Broadway debut)... a place where Wilder now refused to work. Wilder had previously made The Seven Year Itch (1955) at Fox, but by this time was writing/directing hits (Some Like It Hot, The Apartment, One, Two, Three) for United Artists (which offered much creative freedom), and didn't like the fact that Fox studio head Darryl F. Zanuck was forcing director Joseph L. Mankiewicz, to cut down his troubled epic, Cleopatra (1963), and feared he'd be working under similar restrictive conditions. The Seven Year Itch was an adaptation of a play by George Axelrod, later the author of Goodbye Charlie. One would assume that, had Wilder accepted the assignment to direct Goodbye Charlie, his likely co-writers on the film would be both Axelrod (who was then riding high from scipting Breakfast at Tiffany's) and Wilder's main collaborator during this period, screenwriter I.A.L. Diamond (Some Like It Hot, The Apartment, One, Two, Three, Irma la Douce, Kiss Me, Stupid, The Fortune Cookie).
By this time, however, Marilyn Monroe was already dead, so it's anybody's guess as to who would've been "Charlie" in this alternative universe... Wilder could've chosen to re-team Shirley MacLaine and Jack Lemmon from two of his previous hits (The Apartment, Irma la Douce), or perhaps he, too, would've cast Debbie Reynolds, or maybe he'd use Kim Novak, ahead of (or in place of) his film, Kiss Me, Stupid (1964). Interestingly, Kiss, Me Stupid, which was a flop, was notorious in its day for pushing the envelope on what was considered tasteless and vulgar for a Hollywood film. One can speculate that Goodbye Charlie, as co-written and directed by Wilder, would certainly be sharper, wittier and more sophisticated in its humor than what we ended up getting from director Vincent Minnelli and screenwriter Harry Kurnitz (though Kurnitz did previously collaborate with Wilder on the courtroom classic, Witness for the Prosecution), and possibly more daring.
Here's a photo of Jack Lemmon and Shirley MacLaine during the filming of Irma la Douce, and Kim Novak in a color publicity shot for Kiss Me, Stupid (which was filmed in black and white):
For further reading, take a look at this interesting blogged film review/overview of the film version of Goodbye Charlie, largely focusing on its place in the career of director Vincent Minnelli.
Though the various constellations ultimately wouldn't align, for a number of reasons, outlined above, just imagine what a Billy Wilder production of Goodbye Charlie, starring Marilyn and Garner, would've been like... especially just a couple of years after Some Like It Hot! I'd love to see that version!