Well, PbtA isn't measuring your chances of success. It is providing a randomized input to the story in order to generate tension and keep things moving in unexpected directions. The bonuses you can apply in PbtA do represent your ability to 'be in control' as a character though, which is similar to what they do in d20. Anyway, HoML uses the "5 more than required for success" option to give you 'Complete Success' which means you get to achieve the objective of your check without any downside. On a 'normal success' you haven't usually completely dealt with the situation, or it left some complication. I don't have a critical failure rule, doesn't seem needed, though I toyed with it a while back. I think 3 levels is enough, KISS.I did consider rolling a die on the side. Do you mean that you take say a '+' to mean that a 1 or 20 is more severe? That would still be only 10% of the range. What's key I suspect, is to find a way to differentiate the meanings of broader parts of the range. Suggested in the DMG is that failing by <6 has no downside, and failing by >5 has a downside. And that is used in some published adventures. It's just fiddly to implement. With AW the result is a 5 and I know what that means. With the DMG method the result is a 5 and I have no idea what that means until I also recall the DC and subtract 5 from it. Locking the nuance to the result is far easier to apply than varying it by the DC!
It isn't a bad idea, not sure it is less 'fiddly' than the 'succeed by N or more' way though.Looking then at the result on the die. One might picture (for ability checks, not attack rolls) -
In this picture, there are no guaranteed successes or failures on ability checks (accords with PHB RAW), but when you do succeed or fail, that might come with nuance. A feature that might bug people is possibly a disconnect between character skill (its modifiers to the check) and the outcome. Say I am an expert tier 2 rogue, with +4 PB and +3 from my ability score. So I have +11. If the DC is 17 I can fail only on 5 or less. So if I fail at all, 100% of the time that comes with a drawback. Possibly that will drive dissonance. OTOH it makes Reliable Talent more worthwhile!
- die shows 5 or less, a failed check comes with a drawback
- die shows 15 or less, a successful check comes with a drawback, a failed check is just a fail (the fail is the drawback)
- die shows 19 or less, any success is just a success
- die shows 20, any success is an enhanced success
This always struck me as a pretty simple method. A few games have used it over the years. IIRC Bushido has some pretty ridiculous failure consequences though. lol. OTOH Samurai are like gods and get all sorts of crazy power ups. Combat was pretty much a bad idea in that game though unless you WERE a Samurai, it was stupid bloody.EDIT Another method I thought of, drawing inspiration from Bushido, is that if die shows an odd number then the outcome includes a drawback. That naturally scales with character skill. In the case above, our rogue has a 15% chance of fail with drawback, 10% chance of straight fail, 35% chance of success with drawback, and 40% chance of straight success.