The big problem any developer has is aiming a game at a market and selling it well. If they were to retain the style of the original Fallout games (the isometric 3D) then it would struggle to sell as many would view it as very old and out of date. True fans know that a game is more than just the graphics and it is the realisation of the story through the writers ability to convey the game's universe through in game conversation and the events that unfold during play, combined with visual originality that draws you into the game's universe, but the majority of game players don't look at games in this way and will instantly reject a game if the visuals and effects are not cutting edge and draw them straight in.

I personally think the switch from the old style to the one Bethesda have developed is a good move as a first person perspective can be the greatest at drawing a playing into a gaming universe if done correctly. Don't forget that all first person perspective games don't have to by FPS in style of gameplay. Look back to very early examples to prove this. Even games like Dungeon Master and Eye of the Beholder used a first person perspective view point to play the games and they were definitely not FPSs. Equally Ultima Underworld is another good early example of using first person perspective well in an RPG.

I think we will just have to wait and see what the finished game is like to play, but personally from the previews I've seen and read it looks very promising.