The first time I saw this episode, way back in my early teens, I remember walking away from it amazed though I couldn't say why. Having recently seen it again ten years later I finally understand.
The Gargoyles series had a maturity that I've never seen before, or since, and this is one of the best episodes to show that.
City of Stone, as a whole, is the point in the series where everything that has come before, and been alluded to, is explained and the series begins to set itself up for the Avalon story arc. The spotlight, however, is on Demona and Macbeth and how they came to know each other and how they were able to survive for ten centuries.
Their story takes them through two wars, betrayal, an unwilling marriage, an assassination and one scene that wrenches my gut every time I see it. Even so, the real power from this episode comes from Disney's uncharacteristic, but very welcome, willingness to treat the audience as an equal. At no point this episode, and rarely in the series, does the show talk down to the viewer.
In short, while they didn't dwell on the violence, which is also a plus, they respected us enough not to glaze over, or, even worse, omit the fact that life isn't a fairy tale.
Macbeth's part of the story begins with an assassin entering his home to kill his father. Even ten years after seeing it the first time I'm amazed that he succeeds. I don't think I've ever been caught that off-guard. It was the first time I'd ever seen a hero lose. (At this point I'd like to bring up Gwen Stacy to Spiderman fans, which I've learned of since seeing the show.)
What happens next to Macbeth, The arranged wedding of his love to the king, a common occurance at the time, the pact with Demona, the war that followed, and the one that came as a result of the first all scream of necessary evils; however, when Macbeth and Demona are finally given a choice, they screw it up. They damn themselves to an eternity of solitude and hatred.
The scene that haunted the back of my mind for so long is one in which Demona, after having cast a spell that turned the population of New York into stone by night, walks through the streets smashing people to pieces. It ends with her destroying a woman's arms and leaving her to awaken without them.
At the end of the episode Demona is forced to deal with the fact that both of the betrayals she's suffered were her own doing. In the end she deals with it by refusing to accept the guilt.
All told, I believe that this is one of the most powerful episodes of the series. It was probably even a good thing to have seen when I was younger as it shattered the illusions that the good guys can't lose and that right choices are easy, or even easy to identify.
'City of Stone', in my opinion, stands on par with the best episodes of the already excellent Gargoyles series. The only other episode that obviously stands above 'City of Stone' is 'Deadly Force' for its honesty.