In my opinion, above those erotic games just for relax and fap, the art of erotism has two major direction to go, one being love, the other being power.
This game is exactly a masterpiece in the latter, which is pretty rare in the erotic genre. It's a story about desire(not only sexual) and power, about loyalty and betrayal, about scrambles and uncertainty. Extremely well depicted characters, extremely well written dialogues(even if some wordings can still be improved), and most outstandingly, the choices&consequences are incredibly well designed to present the theme of this story. Be warned: the consequences of your decisions might yield unexpected results that can be very realistic and tragical in certain cases.
It's a good choice-based visual novel even without the erotic elements, but it's even a brilliant one with them. "Everything in the world is about sex except sex. Sex is about power." Quoted from Oscar Wilde, well demonstrated by this game.
The artwork is also very charming, but if only some of the sex scenes could be further elaborated. There are certain artworks that seem painted in a hurry with some pretty unpolished curves.
P.S. For those who complain about the bad endings, please note that only games that majorly provide you with sense of accomplishment give good endings when you do "well and correctly" and bad endings when you "make mistakes". However most VNs are stories that the author want you to read and experience, not games that rate how well you do for accomplishing your goal. There's no "wrong choice" or "game over" in this game.