The incarnation of Princess Zelda in The Legend of Zelda: Twilight Princess was a tad dissapointing but one of my favorites. I was hoping her holding a sword for the first time would mean optional co-op, but not quite.
Her role is still mostly plot-only with her being a mysterious but capable helper. But she reveals herself and somehow loses control of her own self.
So she somehow is possessed by Ganon and for the first time you get to fight Zelda. Well a "puppet" Zelda that is.
It's a pretty sweet fight, and I did enjoy restoring her back to her human self.
But I do like how she provided Light-Arrow support in the final fight with Ganondorf.