During the Cold War, many people in the USA worried that one day the USSR would decide it was time for the long-fated final war and send the nukes raining down. (Undoubtedly, many people in the Soviet Union worried that the USA would make the same decision). This fear made its way into our literature for a couple of decades, spawning its own subgenre of postapocalyptic fiction which included such classics and less-classics as The Chrysalids, by John Wyndham, The Magic City by Nelson S. Bond, the later Mad Max movies, and TSR's Gamma World RPG.
With the ending of the Cold War the fear of a wholesale nuclear holocaust has lessened, and our knowledge of the consequences of such an exchange – and the effect of radiation on the world – has changed to the extent that the old stories are at best quaint. But sometimes the old can be made new again.
So it is with Fallout 3 and Fallout New Vegas (I'd presume with the original Fallout games but I never played them). The world of Fallout is one in which the 1950s never ended until about a hundred years later when the Big One finally happened (with, apparently, the Chinese commies being the main enemy). This is the postnuclear world as imagined by comic books and B-movies, with roving Mad-Maxian raiders, giant ants, mutated monstrosities, people wearing strange assortments of armor and clothing scrounged from a dozen different houses, a world where the world tends to gray and brown because things don't grow well near nuclear craters. Here is a world where the last wars were fought not just with nukes but with lasers, plasma weapons, and even capable intelligent robots.
Into this world you enter; in Fallout 3 you emerge into the world from a Vault, a sealed shelter that's kept people alive for over a hundred years since the bombs fell; in Fallout New Vegas, you somehow survive being shot in the head and are nursed back to healt and given a chance to find out what happened and why. In both cases you wander the Wastelands, choosing what you do and how – and making yourself a legend of hope or fear as you want.
Many of the same people are involved with the making of the Fallout games as the Elder Scrolls games, so there is significant overlap of gameplay – both in advantages and shortcomings. There are few opportunities for really personal interaction; this is a world of adventure but not of relationships. One mechanic that is very nice in the Fallout games but isn't present in the Elder Scrolls games is the VATS mode – an automated targeting and striking mode that allows you to do pretty well in combat without having the actual reflexes and skills to do it in the manual mode. And the imagery involved is quite cool.
The Fallout games are by their nature somewhat dark and gritty, but a lot of that depends on choices. One of the elements the Fallout series shares with its source material is that the Wastelands are in desperate need of a Hero, and you can choose to be exactly what they need. You can go from a rookie afraid of a few mutant rats to the legendary Wanderer of the Wastes, someone that Deathclaws fear and that no one in a hundred miles hasn't heard of. Alternatively, you can become a mercenary monster who hasn't a bit of pity in his veins. The game doesn’t shove you into any particular path.
They are fun games, though, if the core imagery is tolerable. Much of the fun is in the bizarrely exaggerated 1950s material that emerges from the background as you wander the Wastes, starting with your "Pip-Boy" combination PDA and sensing data unit. Imagery from old recruiting posters, the sound of old recordings, even the design of the robots you may encounter, the old-tyme music played by the static-filled radio stations you hear along the way, all of these echo the era they are both parody of and tribute to. The America described in the background is TVTropes' "Eagleland" – the shining perfect family of patriots – just a hair off. And it covers every trope of the 1950s future, from laser rifles to flying saucers, mad scientists, powered armor, and giant robots, in addition to the nuclear war tropes of mutations, wastelands, and civilizations of scroungers atop the ruins.
And sometimes it's just fun to be able to take high-powered firearms and blow your troubles away.
Fallout, ladies and gentlemen. Never has the end of the world as we know it looked so… entertaining.