After all the years playing this, I still havent done the imperial cult, legion or house telvaani yet. The imperial cult I doubt I will ever do.

I started both Houses Hlaalu and Redoran, but finished neither. Never played the East Empire Company, but I think I started and finished all of the other joinable factions at one point or another. The Imperial Cult actually isn't bad at all. I found it more interesting than say, the Fighter's Guild questline, for example. YMMV, of course.

Never did the House Redoran quests.

Never did the Morag Tong.

Never completed the Thieves Guild.

Never completed the Imperial Legion.

Only did a few missions for one of the three branches of the Imperial Cult, never touched the others.

Only did the Almalexia side of the Tribunal expansion, not Helseth's.

Never completed the Bloodmoon expansion (Raven Rock got a General Merchant, but not complete).

Still haven't done all of the possible "Mouth" quests for Telvanni, despite having run 3 different characters through the House.

Haven't seen all of the Temple quests from alternate quest-givers.

Still haven't tried several quests for the FG from alternate quest-givers.

Haven't tried a few MG quests from alternate quest-givers.

As much as my characters have done in Morrowind over the course of more than a decade of frequent play, I feel as if I've barely scratched the surface.

Listing quest lines I have completed would be a much shorter list: Telvanni and Main Quest.

Been playing off and on for four years. I have started but not completed the Mages Guild, Thieves Guild, Fighters Guild, Temple, Imperial Cult, Hlallu and Redoran, as well as Tribunal.

I have never started Imperial Legion, Morag Tong or Bloodmoon (though I have briefly set foot on the Isle of Solstheim, but quickly sailed back to Khuul).