I never actually finished Oblivion. I played for ~40 hours and stopped; I played Morrowind 100+ hours, and both Fallouts north of 60. Oblivion was that bad or anything, but it was really dull. Everything was samey and the landscape was like a long stretch of flatland sparsely covered with trees, towns and dungeons scattered about. The dungeons all felt the same too with boring layouts and enemies. Some quests were fun but eventually it got tiring and I stopped.
Morrowind had a varied landscape with creatively unique dungeons and areas to visit and explore. Just from videos, while it isn't as fantastical as Morrowind's, the land of Skyrim is looking much better than Oblivion. Lots of rising terrain, hills and mountains. Towns aren't separated from the world by giant gates. It looks like a real place.
I don't believe any of the radiant AI stuff, random dragon encounters, branching missions, and things like that yet. Regardless, from the improvements made in Fallout 3 and media of Skyrim, it is pretty exciting. Fallout 3 with swords! It's just coming out at a bad time. I don't know if I should wait on Skyrim or buy it to sit in my backlog. Either way, I don't think I'll be playing it when it comes out.