The start is strong. The sex scenes are unabashedly kinky and well written. The story is... well, it is certainly a simplified version of the already simple fairy tale we all know: The miller brags to the king about his daughter's ability to spin straw into gold. As a result, the king imprisons her in his castle, forcing her to spin a room full of straw into gold for three nights, with the promise that he will marry her upon completion of her task.
This story begins at Johann's imprisonment, and we do not even meet the king. Eventually, the king proposes to the miller's daughter, and then we meet some new characters that were not in the original fairy tale, and then the story takes a completely unexpected turn.
This isn't so much a retelling as a completely new story with a couple characters and a scenario borrowed from the Grimm tale. The story was working well up until the ending, which felt abrupt and unsatisfying. I would have liked to see the author keep the erotic angle while staying more true to the original tale, or at least building up to the new ending.