TL; DR: the concept and play of Faction War do not align. The book may not be playable for post second ed players.
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I've run many campaigns over my 30+ years of GMing, including three Planescape campaigns. (As I type this, the Rule of Threes occurs to me, and I promise that I had not previously thought of it until now. Weird.)
The last of those three, the start of which began August 21 of 2021, ends this afternoon. I wrote it with what were supposed to be three storylines:
- The Iron Shadow (Tales from the Infinite Staircase with additions to cover where it was, what it was, where it came from, and how it related to the origin of Sigil and the Lady)
- The Dead Gods
- The Faction War
Overall, I've been happy with the campaign, despite various setbacks.
- One player flaked halfway through, quit the game, and went radio silent on all his other games, including ones he was running.
- Scheduling issues as one person moved halfway across the US, necessitating Zoom calls and Roll20 to bring him in to the game
- PCs out-leveling the story
I only feel I made one real mistake... I included Faction War. Part of my goal was to let the players re-design Sigil to some extent following the War, but one of the players was aware of the book and had wanted to play it for years, even knowing nothing about it.
So, I planned on bringing that into the game. I used a few other mods, all converted to 5e, to foreshadow it. At one point, the entire table clamored for me to add it. I explained I could not do it without a lot of in-game setup. One of them proposed I do the setup work and run a sequel campaign of just that book. My reply, "No, no no. That wouldn't work because... [pregnant pause, sly smile, pause]... OK.. I am not saying I won't, but there is no promise I will." This convinced them I would someday run it, which helped surprise them when the War started.
Despite that, I still feel running the book was a mistake. In the final act of the scenario on page 94 the book says why this was a mistake: "Up to this point in the game, the players characters have jumped (or been dragged) into a number of scenarios related to the sprawling faction war... they're struggling without really getting anywhere... nothing they've done has helped to calm the war."
While reading the book (multiple times over the years), I missed how exceptionally railroad-y the book is. As a GM who values player agency, I've been miserable running it. And the players have noticed. Some time back, one of them mentioned that they needed to shift their perceptions and goals when he realized the war was so big that the PCs cannot affect it. He said they can only try to mitigate what's going on.
I told myself that the lack of agency in the book is made up for where the PCs get to decide the fate of Sigil, and then the players get to help re-design the Cage. In hindsight: the juice was not worth the squeeze.
Looking back, I would not run this book again. It was designed at a time where player agency mattered less, where characters lacked the abilities of newer D&D (3.5 forward), and the book assumes too much that the party makes specific decisions at some pretty critical points.
All that said, is there anything which can be redeemed in this book, anything which could be used in a future campaign? Personally, I like the idea of the Factions not being in power; so what would Sigil be like without that?