Yeah, Whisper is your rival. Kind of like your idea. If you go evil in Fable, she's good, and vice versa.
But what are you stabbing at with the dungeons? You're saying that you can have 2 different paths through it? If that's the case, I think it's pretty sweet! But we still need other quests...And I'm completely changing the story, and adding a little more Fable to it. Anyone want to pitch in?