Even though Oblivion was a great game, the world felt really and I mean really bland. I finished the main quest and stopped playing. I had a great ride, but it was nothing compared to the several hundred hour long ride I had with Morrowind and it's expansions.
I was especially fond of the mixed cities. Combining medieval fortresses with mushrooms, tentacles and other stuff which was quite unique for it's time. With such great looking games it is good to let your imagination run free and create a interesting world, rather than just another bland medieval fantasy world. Dragon Age, Oblivion and probably some more had extremely similar settings with little which really made them unique.
Hopefully they can live up to their promise.