Fallout 1: You played "The Vault-Dweller", with family and friends back home who all worried about you whilst you wandered across the wasteland searching for a water-chip to bring back and save the Vault. The Overseer personally hand-picks you for this assignment. Throughout the course of the game, your dialogue choices are all presented with various predetermined 'tones of voice' and you are given the option to choose from them. You don't get to decide to not be a Vault-Dweller. You don't get to decide which of your fellow 'Vault Dwellers' are friends or foes. The Overseer will always pick your character, regardless of how awful and unqualifying your stats are for surviving in the wasteland. I still roleplayed, happily.
Fallout 2: You played "The Chosen One", a tribal descendant of "The Vault-Dweller" whose people are dying as disease and famine wreak havoc upon the village of Arroyo. You pass through the Temple of Trials, don the sacred Vault 13 jumpsuit, and set out in search of the Holy 13 in the hopes of saving you tribe. Throughout the course of the game, your dialogue choices are all presented with various predetermined 'tones of voice' and you are given the option to choose from them. You don't get to decide to not be "The Chosen One". You don't get to decide if your Aunt hates you or not, or which fellow tribesmen think your being the Chosen One is a mistake. The Elder will always choose your character, regardless of how impossible it might be to even survive the Temple of Trials, to take on the quest for the Garden of Eden Creation Kit and brave the challenges of the wasteland. I still roleplayed, excessively, without trouble.
Fallout 3: You played "The Lone Wanderer", a young vault-dweller from the mysterious Vault 101 where supposedly no-one enters and no-one leaves. Your father disappears without explanation one day, resulting in the declaration of a state of emergency within the Vault culminating in your being forced to flee for your life. Your ultimate goal is simply to find your father and get some answers, although the story does evolve from there quite expansively. Throughout the course of the game, your dialogue choices are all presented with various predetermined 'tones of voice' and you are given the option to choose from them. You don't get to decide to not be "The Lone Wanderer". You don't get to decide if your father abandons you or whether or not to leave the Vault. Your fellow Vault-Dwellers all have pre-determined relationships and feelings towards you which you can do very little to change. The Overseer will always force your character to flee the vault, regardless of how cooperative you attempt to be or how your friendship with his daughter has played out.It is still entirely possible to roleplay.
Fallout New Vegas: You played "The Courier", also known as "Courier Six", a courier in the employ of the Mojave Express with a mysterious past involving characters whom you cannot remember due to being shot in the head. Throughout the course of the game, your dialogue choices are all presented with various predetermined 'tones of voice' and you are given the option to choose from them. You don't get to decide to not be "The Courier". You don't get to decide if you are the one responsible for the events described later in the Lonesome Road DLC, or why a certain NPC harbors a grudge. Benny will always shoot you in the head, Victor will always pull you out of the ground, and Doc Mitchell will always patch you up. The NPC dialogue... even if you use the Alternate Start: Roleplayers mod... will ALWAYS reflect the events of the past. It is perhaps to date one of the BEST roleplaying experiences since the original Fallout.