The writing is really phenomenal, which matters more than you might expect. I don't just mean that it's natural rather than forced, although that's part of it. I mean that the writer went above and beyond. The characters are written as characters, and not just as plot devices whose purpose is to move the player along towards a satisfyingly erotic ending. For instance, the main character loves Samurai movies—it's a detail that 99% of erotic games would never include, because it's irrelevant to the plot. But I love it.