It is a strange animal. It's based on the fairy tale Bluebeard. Bluebeard is immensely wealthy and marries a much young, very poor girl, which lifts her entire family out of poverty. He takes her to his palace and tells her that she may go in any room, except one and gives her the keys. She is the most recent of many wives, all of whom have died. The game is the "Sisters" - different aspects of the Bride's personality, exploring the palace (for the game it can be a mansion, estate, palace or anything else) to determine if the Bride believes Bluebeard to be a good husband or not.
It is a horror game at it's root because Bluebeard's mansion is full of trauma, ghosts of his past wives and often terrifying servants. It is deeply sensual and intimate, I highly recommend the purchase of the PDF at the very least. The book is gorgeous - easily one of the best looking RPG books ever made - but its contents are absolutely worth a read. Having run it a couple of times, I really feel like it might truly shine with a woman as the Groundskeeper - it is ultimately a feminine story, about a young wife and a possibly monstrous husband.