I have yet to finish Morrowind, Oblivion and Skyrim.
Chances that I will play Morrowind or Oblivion again are very little, but I'm currently on a mod-filled Skyrim binge and my latest character might just make it. He actually came close to file corruption earlier today, but my savegame habits provided me with a "clean" save just one dungeon short.
I think I never seriously played Morrowind. I remember buying it on a whim, but when I first played it, I didn't quite get it. But it still made me buy the Oblivion CE, which I played excessively, just never too far into the main story[footnote]depending on if I wanted to deal with the gates popping up everywhere; because if they did, I always felt compelled to purge those daedric abominations RIGHT NAO![/footnote].
Aside from these:
Deus Ex HR; I played a really stealth-oriented character, so I hit a huge brick wall at the first boss battle... Took some time and many failed attempts, and shortly after I finally beat I had no motivation left for the rest of the game. But it's definitely still on my gamer bucket list
Then there's Gothic3, which I almost finished choosing Adanos's ending, but I never went quite through with it. I think my computer broke down that time and I forgot/didn't bother to backup my saved games.
Divinity 2 died under similiar circumstances.