One wild idea would be to have the writers think deeply about what it would mean to be undead and how that would affect your perspective and how it would inform every interaction you have with the world around you. They could use these thoughts to help craft a unique identity for the Forsaken that will make players think about and engage with the concept of differing experiences changing how you value things.
Or everyone can just be generic humans with different costumes on. Only some of them are evil I guess. That works too.