The basis for the setting of Fallout 3 is both refreshing and depressing at the same time -- how many RPGs out there throw you in a world in which a massive nuclear fallout almost wiped out the whole population on Earth except for those lucky few who were in the vaults at the time of the fallout (& a those unlucky few who didn't die from the fallout, but underwent horrible mutations)? We have seen tons of RPGs whose plots are set in the medieval/fantasy era (Neverwinter Nights, Oblivion, Baldur's Gate) and a few good space-themed ones (Mass Effect, KOTOR); however, I believe Fallout can be considered to be in a world of its own, at least in terms of popular post apocalyptic RPG. What makes the setting of Fallout even more interesting is the fact that in the world of Fallout, technology and cultural ideologies actually came to a halt in the 1950s. Hence, the advanced technology that you see in the world of Fallout mirrors what people in the 50s had envisioned how the world would be like in the future. Computers are still stuck in monochrome, radio stations are still playing songs from The Ink Spots, and robots look nowhere as cool as the Transformers.
Then comes the depressing part -- upon setting foot out of the vault, what awaits you is not a world of lush greenery (read: Oblivion), but a vast plain of wasteland. The best one word description I have for Fallout 3 would be "brown". There are not birds chirping in the trees, no rustling of grasses due to the wind. If you set the music volume down and turn of the radio of your Pip Boy, all that you can expect is silence. That, or the distant growling of ghouls or mutants. Bethesda has succeeded in creating a genuinely believable atmosphere for Fallout 3.
Having said that, somehow I had wished Fallout 3 had been a joint production between Bethesda and Valve. In Bethesda, you have one of the best company when it comes to making an open world game that gives the player unlimited amount of freedom when it comes to choosing how they want to go about playing the game and complete their quests. And in Valve, you have arguably the best and most experienced talents when it comes to creating believable, lifelike character models that comes with their own unique emotions, and also a knack for story-telling in real time (i.e. not cutscenes).
All in all, I'm enjoying every bit of the 20 hours I've put into Fallout 3 so far. Sure, there are quite a handful of bugs and stupid AI scripting (which I find it hilarious and see it as a proof that it is a Bethesda game, as Fallout 3 shares so many of the same problems as Oblivion), and apparently there are a few game ending bugs in the ps3 version, which thankfully I've yet to encounter. One gripe though: the radio station is way too repetitive. Listening to GNR for a good ten minutes and you'll find yourself listening to the same old song and and talk from its DJ, Three Dog, whose howling every time he ends his speech started to get annoying. Well, I suppose not all games can have as brilliant a radio soundtrack as that of Vice City.