You know, I haven't played a whole lot of visual novels, but I'm pretty sure what defines the genre is that they basically have no gameplay besides navigating dialogue.I love the VNs that have gameplay, story and love some action and romance.
Well, anyways, my pick is the Black Souls series. First of all, the story is unique and there's not much else like it. The artstyle is usually seen as a weakpoint, as, well, you can take a look yourself, but it adds to memorability. The gameplay goes from "one of the best RPGM games" in the first to "the best RPGMaker game" in the second.
Unlike a lot of other dark fantasy games, the protagonist is usually the offender (assuming he takes the choice to do so). As Mary Sue says, "Rape, kill, cheat and betray".