In Choice of the Vampire, I’m not speaking of just vampires, existing. I think it’s possible to write vampires without them being all that dark. (I’d say Twilight here, but Edward is a creeper.)
In Choice of the Vampire, you’re playing a blood sucking fiend who may or may not struggle with what they’ve become. But that scene, where a group of villagers take one of their own and offer her to you as a slave/sacrifice. I find that chilling, the depths which people will descend to. You’re the monster, yes, that’s your nature. But what’s their excuse? Surely it’s every bit as monstrous what they’ve done. And then the game pulls in the blood-drinking=rape comparisons. There’s war, there’s slavery. Everybody you love dies, generally as a result of knowing you. For me, Choice of the Vampire is dark, as is fitting a vampire game. And since it’s a choice game, you can choose to struggle against that darkness, there are flickers of light, but there’s no happy ending, nothing but just a chance to survive.
Choice of Romance, you start the series possibly falling in love with this charming Monarch, and as it progresses you watch their descent into insanity, until you’re forced into some hard choices of what to do in order to save yourself, your position, and your country. So the game isn’t completely dark, but in that last game it sure did feel that way as I kept trying to find a single good ending without compromising my ethics. But again, it’s not a world filled with complete despair. We barely get to actually see the rest of the world, and we are born into a privileged position.