Let them alternate between each release from each franchise.
Edit: What's wrong with Obsidian? All they missed, in my opinion, was the atmosphere. In those regards, Fallout 3 is superior. Other than that, both games played along in nearly identical manner, in terms of gameplay.
New Vegas had the right atmosphere for the Fallout Series. Fallout is about progression, the rebuilding after a nuclear war. New Cultures learning to deal with one another (War. War Never Changes) Fallout takes place 84 years after the great war, and people already started building new towns and cities. They were farming, both plants and animals, they had a working economic system. Fallout 2, taking place 164 years after the great war, we see a Nation (NCR) expanding into Northern California, people becoming more advanced as they rediscover old tech. Even Fallout Tactics shows people rebuilding, farming and so on.
Fallout 3 had none of that. The Game is set 200 years after the great war of 2077 and yet it looks like the Great War happened a couple of weeks ago. No living trees, no farms, no nothing! People just sat around in radioactive crap holes for 200 years. It was by far the wrong setting for a game taking place 200 years after the nuclear war.
Another problem with it, is that DC was pretty much intact! It was the capital of Pre-War America, it should have been nothing but a radioactive crater the size of DC. Yet all but the white house is still there. When every other city, such as LA, San Franciso and Chicago have been nuked off the map. Even Las Vegas, though it was spared from much of the nuclear warheads that were aimed at it. The City still degraded and fell apart, over 200 years. Mr.House came along and fixed up the Strip, while everything else was taken back by the desert.