I think the decision I spent the most time on when preparing my Fallout game was choosing a system. I knew that my game would have fighting, exploring, faction politics, and resource management, so my rules would need to support those things. Also, my game would be online and remote, so I wanted a game my players could participate in even if they didn't have a copy of the rules. This is where the official Fallout RPG fell down: it didn't look like character creation would be possible without everyone having a full list of all the character options, which is a sizable chunk of text.
Eventually I started to think that it would also be cool if the game had some of the mechanical elements of the video game: specifically, percentile skills and action points. That decision led me toward Mythras, a game which evolved from Runequest, and which, sure enough, has percentile skills and action points.
Over the course of the game, though, it's become apparent that Mythras wasn't the right choice for me for the following reasons:
I found the combat rules too verbose, vague in cases where I wanted concreteness and limiting in places where I wanted flexibility. Much of the built-in flair and tactics are built around hand-to-hand fighting, not firearms combat, which is the opposite of what I need for Fallout. In practice I've thrown out, simplified, or rewritten many of the rules to get it in a form I feel comfortable with.
Enemy stats are extensive, which means coming up with new enemies is time-consuming. Given that I had to stat up a bunch of Fallout creatures by hand, cranking out a big stat block for each creature was far more work than I felt like doing. In the end I chose an abbreviated stat block format that gave me what I needed to run a fight, and that I could fill out with just a few moments of effort.
I thought Mythras's rules for diseases and poisons would work for radiation poisoning, and they sort of do, but not in the way you would expect for a Fallout game. In Mythras, poison effects are based around saving throws, and you either suffer the effects or not based on a die roll. For Fallout, you want something more cumulative, where the effects build up over time.
I wish now that I'd chosen an OSR/NSR game, given that Fallout, with its strange ruins and hazardous wastelands, is basically classic D&D anyway. A game like The Black Hack or Pinkhack would have given me simple characters, simple combat and simple enemy stats, and abstraction of resources so I could have the tension of running out of ammunition without all the bookkeeping.
My runner-up choice is the Cypher System, which would have been flexible enough for post-apocalyptic play, with fight scenes that aren't cumbersome. Cypher's character building blocks would have allowed human, mutant, and robot PCs without additional game design on my part. Monster stats can be as simple as "this giant ant is a level 4 creature." Plus I could have used cyphers (the single-use gadgets in the Cypher System) to support some Fallout concepts like chems and magazines.
In summary, I would have been happier with something either simpler or more flexible for this game.
In the next post, I'm going to explore the setting prep I performed, in contrast to the prep I should have performed.