The vault you begin the game in, Vault 101, was built to remain permanently sealed. TV screens and the intranet still bombard everyone with messages about how dangerous the outside world is some 200 years after the war. The idea of Fallout’s first hour is to embed that single idea into you before you leave. To make you relax into the vault’s claustrophobia, to make you believe it’s your home, to imbue you with the same sense of paranoia as its inhabitants.
That way, when the plot finally sends you out into the scorched Earth, you feel a sense of trepidation. Think of that incredible moment in Oblivion when you leave the sewers and step out into the sunshine. Imagine that, only with a foggy, uncertain sense of dread. That’s more, much more than Oblivion with guns.