Its not an issue of it being the same, but have the game reach a natural evolution so that it would be still on par with current games yet still give an accurate reflection of its previous incarnations.
For example, the issue of Turn Base Combat. Now I am not expecting it to be solely turn base like Fallout 1 and 2 was, however real time is right out. The most viable option that would cater the actiony people and those who are traditionalists would be a toggle between turn base and continual turn base as is in Fallout Tactics. That is one of a few things Tactics did right. Another issue is Isometric view. There is no way in hell a 2D game is marketable today and I am fine with that. The best option would be to have the game in full 3D render, as in Oblivion, but with full camera control and camera options as is in Neverwinter Nights 2, plus a toggle fo those who prefer first person view. With that style of camera options they simply cannot lose because it would be completely malleable to the player's needs and gameplay style.
Those are just two examples in which the game can be completely marketable and using today's technology while at the same time still pay homage to the original Fallout CRPGs.