I want to look at your question objectively.
Lets throw gameplay, story, combat system, UI and everything else out the window here. Lets just look at the genre and their concepts and the game scope.
Literally when you are the only studio in the world who makes a game like this. Meaning you can't look at someone else and see how they do it differently. At some point aren't you just refining til you get it right?
ES games are ahead of their time. We still live in a world where people care more about particle effects then they do believable game worlds. So in all honesty I see alot of refinements in this game that weren't in oblivion. The game world logic is better, there is more that goes on in the world, weather systems are more organic, there is a list of things I can point out.
Bethesda isn't making a video game, they are making a virtual world, go play any AAA game this year and come back to skyrim and I dare you to tell me you don't see the difference.