JC Winchester does a lovely job of detailing the transformation from David to Amy, complete with the unusual details (or order of details) that personalize the experience. Similarly, I loved the mental and emotional transformation, especially later in the story when those gender lines become somewhat blurred.
I have already said what this is not, but what it is is a story of social and sexual experimentation. As erotic and kinky as it is, the story never simply reduces the crossdressing experience to a fetish. It is a part of Amy's self-expression, and that blurring of gender lines that I mentioned is what moves the story forward into something romantic.
Come for the Crossdresser's Night of Thrills, but stay for the dream of a happily ever after.