A little bit of history
My first experience of Fallout was a pirated version of the first game. It was bundled with Diablo and something else that I can't recall, and was missing all of the FMV cut-scenes, voice-acting and so on (I feel I should point out that I was living in a country where there was very little access to legitimate copies of PC games, and PC shops would openly sell pirated copies very cheaply).
Right off the bat, despite missing out on some of the background information due to missing content, I knew I was going to love the game. Nothing I had played to that point had built such a fascinating and alien world. Built from the destruction of a nuclear war, the game is set in post-apocalyptic California and incorporates a mixture of 50s sci-fi technology, Mad Max and more. For an RPG, this was new and exciting for me, as the previous RPGs I'd played were almost all in the "high fantasy" category. You play the Vault Dweller, who had lived a sheltered life in a vast underground hi-tech bunker. A malfunction with the water purifier leads you to be chosen to leave the vault (the first for a very long time) and find a replacement water chip. The adventures you have affect more than yourself, and the decisions you make create different outcomes for the various communities you encounter.