Elder Scrolls games are a funny one.
Oblivion was fatally flawed - it had a tedious main storyline, indifferent voice acting, and the world's worst levelling system. The problem wasn't just the levelling itself - it was the fact that World levelling meant that after a while you couldn't walk outside a settlement without getting attacked by a frigging minotaur - and bandits would be wearing priceless glass armour, leading to the question why they bothered with a life of banditry, when they could just sell their armour and would be made for life. This sort of stuff really killed immersion.
That said, I loved the Shivering Isles expansion.
Skyrim was certainly a better game; at least they crafted individual dungeons. That said, a large part of the quests and storyline were terrible uninvolving. It felt so... generic.
Despite it's terrible combat and insane crafting/spell progression system, for my money, Morrowind remains the best, for no reason other than it presented a genuinely fascinating fantasy universe. I genuinely came to love the Dunmer, those xenophobic gravel-voiced loons.