Promethea 12 was something of a watershed moment for the series. Previously, the series had been very well-written, with excellent art, but it was still "just" your standard superheroics. This issue is when we first realized that it was going to be something more.
Here's an interesting panel layout trick, courtesy of Alan Moore and J.H. Williams III. In this two-spread, the panels can be read either clockwise or counterclockwise, and in either direction they'll make sense as a sequence and conversation.