I played Morrowind and Oblivion and even TES II (for an hour or so), But finished none of them. I quit both games right before or at least quite near the big final battle.
Morrowind: I found a crappy shield (with a name) in a random cave. And sold it, because it was crappy. Days later I learned that this legendary shield was a quest item.
Oblivion: I discovered that all the thanks you earn for brining the corrupt officer to justice was a warm handshake, 100 coins and a rusty dagger. Every bandit has more money. The quests may be interessting, but without proper reward I lose interest.
Because I am quite greedy, I was super rich and very powerfull half the way through the story line. You know you are strong when Dreamora Lords and ogres ambush you on a highway. And common bandits wear glass armor or better. When you spend more time running between the dungeon and the next city to sell all the stuff than actually questing, exploring or dungeoneering, it gets old very fast.
Because of that - and because my PC is so old that Oblivion is only running with low resolution - I will wait a while before I buy TES V.