So, after this question pointed me at that hack, I convinced the group I GM for to try out a campaign with Descriptive Damage. I'll describe our experiences so far, though they should be taken with three caveats: (1) all of us are still comparatively new to Dungeon World, so things might play out differently with a more experienced group (or at least a more experienced GM), (2) we've only played two sessions so far, and (3) the hack left many details up in the air, and different decisions on our part might have led to a very different game.

Preliminaries: Our Rule Selections and Interpretations

• We played with Resist Harm triggered by any injury to a PC. Damage to monsters was as in regular Dungeon World.

• We played with standard HP totals and HP regeneration at a rate of half the character's class's bonus HP per level-up. Magical healing was as in vanilla DW. I did not use HP handouts to incentivize "doing fictionally and thematically relevant things".

• We did not cap HP expenditures.

• A character protected from an attack by armor took +1 to Resist Harm. A character impervious to an attack because of armor took +2 to Resist Harm. (We also considered abstracting away armor ["…if you have lots of hit points, it's because you're badass and probably wear heavy armour"], but the first encounter was with a razor boar, and it helped to have the monster's fiction backed up by some mechanical consequences.)

• Spell Defense was treated as giving +1 to Resist Harm.

• We didn't use monster "deadly" ratings. Injuries were deadly or not as adjudicated from the fiction.

• We couldn't figure out whether Last Breath was supposed to be in-play or not, so, as a death-adverse group, we kept it in. However, it hasn't come up yet.

Aspects that Played Well

Specifics for Injuries

Playing without Descriptive Damage, our group often has good fictional detail on the how of an injury, but fewer specifics the what; with Descriptive Damage, we got both, even though none of the injuries I threatened were particularly exotic. For instance, our cleric, instead of just being beaten and bruised, has a nasty gash in the shoulder of her off arm that got infected when she fell into some filth, plus she's dealing with some lingering effects from a concussion. Our druid got stomped on by a gargoyle while in snake form, and now she has some broken ribs and a crushed lung. Our wizard broke two fingers when another gargoyle wrestled a book from his hands. Etc.

Threat Differentiation

Since character's injuries were specific, the fiction picked up situations where certain monsters could exploit or exacerbate those injuries, making those threats play differently than indiscriminate ones. For instance, after slicing her shoulder, our cleric was still willing to get in a tangle with a roper since it was just trying to eat her. But she was a lot more skittish around a pack of gargoyles that could see and target the rent armor on her left side and her mostly useless left arm.

Balance and Player Spending Strategies

In the hack comments, Paul writes:

Realistically, if you want to be doing basically OK, you'll probably want to spend enough hit points for a +3 on each roll.

This was our experience. Most of the time players spent 3 HP (for a 1/12 chance of missing) but they were willing to put up more if they felt that avoiding the injury would let them wrap up a battle. So, roughly speaking, injuries under Descriptive Damage corresponded in magnitude to damage from a solitary monster with a damage die around 1d8, though, because of player agency, with much less variance. At least against solitary monsters, the game balance didn't feel like it shifted much.

Aspects that Played Poorly

Confusion about "React Immediately"

One of the choices for Resist Damage is:

• You maintain your position or advantage, and can react immediately (if you do, take +1 forward)

In the first session I read "react immediately" as a bonus to give a character: little or no in-story time would pass between their injury and their next action. This played a little oddly.

For instance, one of the times our cleric went for the razor boar with her mace, she missed, the boar inflicted an injury, and she rolled an 8 and chose immediate reaction, which she used to Hack and Slash the boar anyway while she was being gored. Characterization-wise, that was cool, but it made the H&S outcome more like a 7–9. And if she had rolled 9 or less on the second attack, I would have had to come up with another way for the boar to deal damage, which could have triggered an immediate reaction….

Reviewing for the second session, I came away with a different impression based on the paragraphs before the move. Instead, I read "react immediately" as a character's usual ability to keep taking actions through a scene and the absence of "react immediately" ala the Frodo example. That led to less dissonance between the fiction and the mechanics.

HP Mechanics that Crossed the In-Fiction/Out-of-Fiction Line

We had a lot of difficulty agreeing on whether or not HP corresponds to anything in the fiction, mostly because either choice led to immersion problems.

HP as "Plot Immunity / Mistake Potential", Paul's likely intent, while supported by the hack itself, interacted jarringly with other DW rules, particularly ones about healing: HP outside the fiction but HP management in the fiction makes for disconnects between player and character motivation. Clerical healing, as mentioned in the hack comments, is the trickiest case, because it's unclear story-wise what the cleric is doing or why. We also didn't know quite what to do with potions, and our halfling druid had to invent a justification for singing her healing song in the middle of the night out in the woods when the party was trying to avoid attention.

On the flip side, attempts to equate HP with "Defensive Combat Skills / Stamina / Luck" presented problems with the hack rules not being designed for such equivalences. Skills aren't really something that threats of injury consume; stamina is something that should also be depleted by other actions and replenished by rest; luck normally applies to more than just injuries. One might be able to swing an explanation that uses a kind of divine favor or luck specifically for self preservation, but I feel like it makes more sense to rethink the DW HP rules to fit the hack than vice versa.

Deaths by a Thousand Cuts

While differentiating monsters by threatening different injuries works well for the heavy hitters, monsters that wear PCs down slowly don't seem to work well under Descriptive Damage. Or, at least, I don't seem to be clever enough to describe injuries that players want to spend just 1 or 2 HP on. As a consequence, those monsters become a lot more dangerous.

I think part of the problem is that I always gave injuries with all three kinds of effects: immediate, temporary, and lasting. If I only threatened one, say, then hopefully players' spending would be motivated by their chances to reach the 7–9 category instead of the 10+ category.

Aspects that Played Differently

Duration of Consequences

Under Descriptive Damage, injuries are about equally frequent as in vanilla DW, but their consequences are a lot longer lasting, especially because Recover from Trauma can have some steep time costs and still not provide a full recovery. In our game the party has just barely uncovered one front, and already every character has at least a few months to wait if they want to heal naturally; it takes some believing that they're not packing up and heading home. I may rule that a potion erases an entire injury, or else we'll end up with a much grittier feel than we normally like to play with.

Yes - Not just with your GM, but your fellow players too.

First of all saying it's not Dungeon World if there's pre-prepared material is silly. Common modes of play with DW include Dungeon Starters (minimal), Adventure Starters (more form), and Adventures (even more form); see this site for an example list. There's a whole section in the back of the rules for adventure conversion from any trad D&D adventure to DW. So your GM isn't a priori doing it wrong because they are adapting an adventure.

But more importantly, in a collaborative game of this sort, it's easy to make the game result a bizarre mishmash that the other players don't like either if you make campaign-changing decisions without consulting them. There's "going off script," and then there's "going off campaign premise." While DW shouldn't be scripted, it's also a major shift to say "let's change the premise here from us being the champions of the... Gods?" to being "let's be rebels on the run from the gods." I can see another player being upset by that and really not wanting to go along with that change.

Your GM should be able to adapt, and his prep won't be ruined by this - he can always just use those allied NPCs you were talking to as the "hunt you down NPCs" now. But it's not his prep you should be worried about specifically, it's the entire group's fun (GM and players). So when thinking about a major "campaign changing" twist, I think it is indeed in good taste to put it out in front of the whole group - GM and players - and say "Hey, do we all think it's cool if I do this?" so you don't ruin the fun for others. And if your GM does turn out to be relying on prep more than DW "purists" would have him do - well, he's the GM you have and that's the game you're in, so this presents an opportunity to get that out on the table and discuss it if it's an impediment.

One of the things about a more narrative game like DW is that you don't need to be relying on "surprises" and such, discussing how the game will narratively flow from here is completely acceptable.