It's interesting, while very compact. I suggest to add a 2nd pamphlet, keeping the 1st for the Watchers and the 2nd for the Abyss.
About the second pamphlet, I suggest to add a dozen of possible "Truths about the World" that could be used for inspiration during the exploration of the deep (with hints or clues for each one, easing the creation on the fly). Those truths are useful for the character's advance.
Also, you could put for each level some notable/interesting area, suggested dangers etc. so the Abyss would have useful sparks for the adventure.
Also, I think we need at least an example, or a longer explanation, about the resolution system. I mean, let's take the first level, the Mines; let's say that I have 4 Watchers to my table. So I have 4 points of "Hordes".
- They of course say that they want to descend quicly along the mines... What I should do? A roll for everyone to navigate the deep? A roll for just the first of the Watchers? No rolls at all?
- Now let's say that I decide to spent 1 Horde to "stop" them. Ok, so they find a host of deformed men with the skin partially turned to stone, menacing them with simple weapons. They could try to avoid them, or beat them, so probably we will have some roll.
-I see there are 2 "enviromental" threats for Level; I think it could be interesting to spend Horde points for generate an eventual additional threat to be surpassed, instead of hordes of enemies that "block" the passage.
- Also, how / when I should show the Idol of that level? I just should put it at the end, before letting the players to descend?
- How many rolls I should deserve for the Idol? 1? More? 1xWatcher?
Then: for what I see, at the 6th Dusk mark the adventure is lost, so the players can make less than a long rest for level, correct?