Elder Scrolls: 7 Reasons Morrowind Is BETTER Than Skyrim
1. Morag Tong > Dark Brotherhood
While the Dark Brotherhood questlines in Oblivion and Skyrim are nearly universally-beloved, I've always found the idea of "legally-sanctioned roaming executioner" a more satisfying and unique role than "member of a secret brotherhood of assassins" (we've been there, done that, so many times).
The Morag Tong feels specific to Morrowind - and, based on the in-game lore, that's because it is. While the Dark Brotherhood operates all over Tamriel, the Morag Tong are an institution of Morrowind, not the empire writ large, and that specificity lends it a uniqueness that I've found lacking in the Dark Brotherhood quest lines.
I always got the feeling that the pitch for the Dark Brotherhood was basically "killing people for money is fun!", while the Morag Tong has a much deeper, more complex history, structure, and philosophical viewpoint.
Plus there's something to be said for the satisfaction of seeing a guard charge at you pell-mell, weapon drawn, only to pull out your writ and let him know it's all cool, you're on the same side. It's the subtle touches that make Morrowind great, and the Morag Tong quests exemplify that subtlety.