Playability, humour, exploration, atmosphere, dialogues, mystery. Cavalier-oblique or isometric perspective. Has anyone ever thought that in lack of the classic Fallout saga expected continuation, the community could actually make oneself such? It is certainly not unachievable. The engine, the less fancy, the better. Keep it simple, keep it smart. Maybe even browser based. What would be truly constructive, is for the fans to be able to submit their random encounter scenarios, their dialogue writings and otherwise creative suggestions, to go a deeper level in participation with the world creation. This way, we could end up having something genuinely rich, eventually.
Just a loose idea. Take it or leave it.