I was interested in Nyssa at first, but in the end her character didn't work for me and I ended up disappointed. I mean, at first I could sort of sympathize with her, but then, like you said, she turned out to be more or less psychopathic, at least that is the only explanation for her behavior that I can see without rereading and looking for more clues I might have missed. IMO Gotham has enough villains who are insane, and I've always like that while Ra's is extremely ruthless and has more or less genocidal objectives I can (at least when he's handled by good writers) see his rationale and objectives. And I agree that this series made Talia less interesting and strong. I always liked the conflict in her loyalties, and think that was better than having a double feature villain with her and Nyssa together in the cult.