Humanity rebuilding and adapting after the disaster it created for itself - and not learning from its past mistakes. A depiction of the society and its means to manage, for better or for worse. A game that does not thrive on random combat, but storytelling, quality writing and players impact on the events according to his/her choices.

I also consider the the original gameplay/RPG mechanics to be part of what makes Fallout Fallout. It was created as an RPG (and quite heavy handed at that) and that is what it should('ve) remain(ed).