The realm-level of play is what originally drew me to the Birthright setting. The concept of realms, holdings, domain actions, realm magic, regency, etc... was very interesting, and still is. Then I took on liking the unique elements of the setting: generally low in magic yet the available magic is pretty powerful, the bloodlines, the awnsheghliens, the specialty priests(when I got to the part about the clergy, I really loved how they handled the gods and their priests), the human subcultures and the other racial uniqueness, etc... I'd say the whole setting has become a passion to me.