This was an exciting episode from the opening battle between Katya (the demon, dressed in black) and Nina (the guardian of Pandora's box, dressed in white). The outcome of the battle was ambiguous, leading to a nice twist. Throughout the episode, just enough was revealed and just enough hidden to build suspense and keep the audience guessing.
The minor characters were better developed than one-episode characters usually are. Hope's confusion, disbelief, and distrust in the face of magic were convincing. Her youth and inexperience combined with her self-reliance and strong will to create an engaging heroine, one who seemed fit for her destiny as the new guardian of Pandora's box.
Katya was a smart demon who tried to persuade Hope to open the box before resorting to force. Zankou would indeed have been impressed by Katya's skills if she had survived. But she fell for the same trick that she herself had used on the Charmed Ones. It made for a satisfying vanquish.
Pulling it all together was a theme of self-discovery: Hope finding her destiny as the guardian of Pandora's box; Paige learning that she can be Charmed and also have an identity apart from her sisters as a Whitelighter; Wyatt using magic to assert his independence; Piper and Leo struggling with their role as parents of a magical boy. And foreshadowing events to come, Phoebe showed her propensity for psychological analysis: she suggested that the ringing in Paige's ears might be psychosomatic, and she deduced from "Darcy's" behavior that she was not who she appeared to be. Even the demon Katya was motivated by a desire to fulfill her potential and assume her rightful place in the demonic hierarchy.
Complex and rewarding, this episode demonstrates that a light drama with a magical premise can be more than a guilty pleasure: it can rise to the level of art.