The originals have less content? How come?
Well kind of they just did, have less content than Fallout3, would anybody disagree with that ... they may have just
seemed bigger than they were because of having to take turns in combat, board-game style, that dragged out the game-play time.
But if wanting board-game combat play, go for the early Fallouts, if wanting role-playing with movement as a real person would move in combat, then leave out the early Fallouts.
Early Fallouts were enjoyable at the time that they came out, being new and a ground-breaking kind of play, but Fallout3 has taken everything so much further, it's massive, taking turns would kill the game, and most are into playing a role now as realistically as possible.
There's plenty of dialogue in Fallout3 to explain what the game is all about, and each group also tells you what they are all about, making the early Fallouts not a necessity for understanding what the game is all about.
Fallout3 will be closer to the previous Fallouts nuclear-apocalypse-wasteland scenarios than Fallout New Vegas is, which I understand has now quite a lot of civilised development in the scenario. Fallout3 does have developments, of a kind, as groups struggle to survive as best they can.
So wasteland-wise canon-wise Fallout3 I would say 3 covers the early Fallouts better.