How easy the battle was made it all the more frustrating when he "cheated" afterward. Getting to fight the guardian hearltess would've been fun, I think.
I think most of playing as other characters was fun, because it gives you a chance to go through the same missions in entirely different ways. The only really frustrating one for me to use was Xemnas for certain weapons, mostly because of his aerial attacks being aim at the ground.
I really wonder if she had a reason to not want her heart back. She just wanted power, like Marluxia, after all. It would be interesting if something happened to change her into the cruel Nobody she was.