The most amazing game
The game is set on the East Coast, rather than on the West Coast like the first two games, providing Bethesda with a perfect opportunity to tell their own story. To show different communities that have formed on the East Coast, how they've adapted to the harsh new reality and managed to survive, and what problems they've caused and now face. Instead of this, Bethesda decided to populate the East Coast with the already familiar super mutants, Brotherhood of Steel knights, and Enclave troopers. Unfortunately, these groups left their depth over on the West Coast and have all the complexity of cardboard cut-outs.
Super mutants, the failed attempt to create super soldiers from normal humans, are now flesh-eating beasts keeping gore bags full of body parts as handy snack bags wherever they hang out.
The Brotherhood turned from an almost monastic order, too small to fight the super mutants on their own or to attract too much attention to themselves, into a holy order of knight-protectors keeping humanity safe and shooting at things on sight. In Fallout they didn't have enough equipment, in FO3 (100 years since Fallout and 200 years since the war) high tech weapons and armor are everywhere and fallen comrades with their Power Armor and laser rifles are left behind without a second thought.
Although the game tells you that it's been 200 years since the war, the gameworld and environments indicate that this is a lie the Matrix wants you to believe and that it's been only a few decades at most. Electricity, pre-war electronic equipment, powered and still working computers (just think about that for a second), working cola & snack machines, weapons, ammo, scrap metal (needed by many), and even unlooted first aid boxes are everywhere.