Some interesting things about Fallout: Equestria (spoilers, kind of): * The reason for combining Fallout with My Little Pony was to show that it doesn't take terrible people to do terrible things. The point was to take the sweetest, most innocent creatures, and show how they could be changed, and end up murdering and raping each other, without it being anyone's fault. * One of the side-stories is that the main character gradually discovers the causes of the war. At various times, you place blame on Pinkie, on Fluttershy, on the zebras, and on others. Eventually you find out that it wasn't anypony's fault. Everybody acted as you would expect them to act, and it was mostly dumb bad luck that brought the apocalypse. There was no villain whose assassination would have prevented it; one character even attempts a royal assassination, which fails; and another character later points out that it wouldn't have made any difference had it succeeded. There were just a number of minor stupidities that snowballed. * In other fiction, the protagonist is in a situation that grows more and more desperate until the climax and resolution, when everything is resolved. In FoE, after the initial disasters on leaving the Stable, the heroine's status, love, power, friendships, and wealth gradually increase, making her more and more comfortable and providing more and more temptation to just stop and let somepony else worry about saving the world. At the story's climax (which is executed poorly, but the concept is brilliant), the last temptation is that the heroine's own goddess, whom she has looked to for the strength to continue on, confronts her and tells her to turn back because she has done enough and the ponies she is trying to save aren't worthy of her sacrifice. * The capacity for violence is necessary, but also very dangerous, and things can spin rapidly out of control - and not in a ham-handed "he went over to the dark side" way. * Characters are not conveniently faced onl

I have read all of the original. It is a very well written work, but as befits Fallout, it is grimdark. There were many parts which seemed like they wouldn't have been nearly as enjoyable without strong familiarity with the Fallout universe. They cross it with MLP very well- some of the combinations are eh, but several of them make perfect sense, and are very tragic. I'm not quite sure I would describe it as "rationalist"- the protagonist is clever, the enemies are often clever, and there's a little bit in the way of plotting and puzzle solving. It seems much more like a standard post-apocalyptic adventure than rationalist fiction, but I'm not quite sure where I would draw the line around rationalist fiction.