To me Oblivions quests seemed to be more fleshed out, with more emphesis on creating "mini" stories, rather than more arbitrary quests (not implying that all Morrowind quests were like that). But that might just be me :shrug:
This is exactly what I call
quantity over quality, because although it might seem some of Oblivion's quests were more detailed and longer than average Morrowind quests, they lacked the intrigue, under current, rivalry, and gray morality that was interwoven in the Morrowind's quests. Except for example the dark brotherhood quest-line and some misc quests, I know.
The reason that a lot of people like Morrowind over it's predecessor and successor is that it was different, from any other experience that we had in any other game, it was dreamy, intriguing, hard to start, but utterly more satisfying to conquer. It was a surreal life never experienced before or after, not as generic as Daggerfall's randomly generated environment and encounters, and not as bland as Oblivion's repeating landscape and encounters.
Not as overwhelming and hard as Daggerfall's world and game-play, not as underwhelming as oblivion's environment and the deeply rooted hand-holding in every aspect of the game design, and cut down quest meats because there was not enough resources and man power to make a lot of voiced dialogs, so that made the core of the game-play a shallower experience.
Just a perfect middle point for any of those aspects, except that for some people it was hard to get into, as they were not prepared to the game mechanics, and did not know the tricks of the trade in such an open ended game with so much pitfalls.
I do not say that in every aspect it was a better game than the others, but I say it had a better overall experience from the combination of those aspects, and had less compromised elements.