Dad built a water purifier that didn’t work, for people that didn’t need it, and then made it release radiation it shouldn’t have, to prevent it from falling into the hands of people trying to fix it. This killed the man who had no reason to sabotage it and didn’t kill Colonel Autumn, who had no means to survive. This put the Enclave – an army with no reason to attack – in charge of the purifier, which was of no value to them. Then the player entered vault 87 to recover a GECK, a magical matter-arranger that they shouldn’t need and that would be better put to use in virtually any possible manner besides fixing the purifier. Colonel Autumn, who shouldn’t be alive, captured the player with a flash grenade that shouldn’t have worked that was thrown by soldiers who had no way to get there. The final battle was a war between the Enclave and the Brotherhood of Steel, to see which one would get to commit suicide trying to turn on the purifier that neither of them needed. This resulted in more sabotage that threatened to explode a device that shouldn’t be explode-able, ending with the death of the player character, who had the means to survive but didn’t, and who was never given a good reason for doing any of this.
Keep in mind that what I’ve outlined here isn’t even the worst stuff. I skipped over Little Lamplight, Dad’s Vault-killing adventures, and the fact that the writers didn’t seem to notice all the ways that supposed good-guy Three Dog is actually a monumental selfish, delusional, self-aggrandizing asshole. I’ve just stuck to the crucial elements of the central premise and story.
Sure, you can find a couple of plot holes in Fallout 1. No story is perfect, and it’s hard make big stories hold together over the long haul. But this isn’t just “a couple of plot holes”. This isn’t nitpicking, over-analyzing, or looking for things to complain about. This is a story in which every single aspect of the setting and characters was fundamentally broken from inception. What we’re told isn’t supported by what we’re shown, none of the characters pursue their goals rationally, and the player is constantly obliged to make nonsensical choices.