I just discovered this obscure, flawed little gem from the early '80's for myself. The TG element doesn't kick in until the last five minutes, but IMO it's worth the wait.
That said, the transformation itself isn't anything special - we don't really get to see much at all, to be honest - but it's the protagonist's desperate, pitiable performance (by actor AND actress, playing the same character in the same scene) that left the biggest impression on me. It's difficult to describe, but this story scratched a very specific itch for me: A sad loser "hero" who undergoes a transformation into a beautiful woman only to suffer an ignominious fate, complete with a melancholic atmosphere of encroaching doom and oppressive dread.
It's no masterpiece by any means, but some of its ingredients really stand out. It's available to watch for free on Youtube, if you want to give it a whirl.
https://www.youtube.com/watch?v=B3UU8POkTiE