I don't think Oblivion is that bad. It was my first TES-game, and I had a lot of fun with it. Sure, it had some flaws, especially with the balancing and level/world design, but compared to Skyrim, it had much more intersting quests. Most side quests were above average, and some (especially the thieves guild quest where you are locked in a house with other people
) were really one of the best in the whole series. And I didn't even mentioned Shivering Isles, which had even better quests.
Maybe bethesda was afraid to include such "strange" quests like lin Oblivion in Skyrim. But it seems bethesda made the same mistake many other developers did when creating a sequel: they concentrated on the flaws of the predecessor, but neglected the strong points of the prequel. (there are many examples...)