Fallout 1 is about a hundred years after the bombs were dropped and you see how much humanity has degraded. You also see small villages and towns under constant attack and have little trust for outsiders. Take Junktown and Shady sands for example. So supplies are limited and there is hardly anything production.
In Fallout 3 it looks like the bombs were dropped yesterday. Buildings aren't picked clean. There is an abundance of weapons, armor, drugs, and ammo. Everyone looks the same and everyone has the same body type as far as humans go. Everyone trusts you and treats you like a celebrity who is hear to save the day or ruin it. In Fallout 1 no gave a stuff who you were.
In Fallout 1,2, tatics, and nv side questions actually help in the story and play a part in the end. In Fallout 3 there were too many quests were you walked far and just killed stuff at the final destination. The ending for the Old games was based on your actions and told you how your actions affected each settlement, group, person, and faction. In fallout 3 you either got "you died, the water is now clean" or "you died, the water is dirty still and people are sick". DLC's didn't make a difference.
So now for the more wastelandy thing. So in fallout 1 you settlements built in the ruins of the old world, cities built from scrap, and raggy clothing, rusty weapons, makeshift armor, and ramshackle cars. So after fallout 1 technology is slowly rediscovered and governments pop up leading to a genre called post-post apocolytpic which is a genre about the events way after an apocolyptic event. So you see more shiny stuff and a less post apoc world as seen in New Vegas. In fallout 3 there is just garbage, ruins, raiders everywhere, and the bombs didn't vaporize anything.
What else can I can I pack into this rant? Oh yes the lore, gameplay, and fanbase. Go read the wiki and you will see plot holes and how beth didn't care for the lore. It's like letting Infinity Ward make a Mario game, but with guns, linear gameplay, boring storyline, and gameplay not ever similar to a sidescroller mario game. So it was a game made to appease to the Bethesda fanbase. If you compare the stories to the previous games to fallout 3 you can see that they ripped the story off from older games which shows how lazy the story team was when they made the game.
Feel free to keep your opinions about Fallout 3, but listen Fallout 3 does not feel like or ever will be a true Fallout game. Bethesda should have just Fallout 3 into its own game rather than barrow material from Fallout itself. If you don't like turnbased games that is fine, but don't take Fallout 3 as the almighty game that invented wastelands or something that is fallout.