Add a bit more spice to the RPG aspect of the game. I find Morrowind's world amaizing so quests, weapons, clothes etc. don't really make much difference to me (although the odd new weapon or armour may be cool).
Really just looking for stuff that adds that little extra spice without destabalizing or butchering the game.
Couple of mods that I like to use for role playing purposes are;
As I put before LGNPC (lots of little tasks and backstory for npcs)
Morrowind Come's alive. More for the companion selection.
As before Morrowind Crafting. Handy for if you want to have a reason for taking your time and improving mercentile and speechcraft. A good motivation for travel also. You can make a
lot of different things.
Romance mod. Gain (and possibly loose) a partner, have kids that need to be taken care of, prostiture yourself. Add's some well handled and not tackily done features that are good for rp options.
Stormrider. A boat, well more a small ship you have control over. Goes well with Morrowind Crafting for transporting goods for sale. Nice for travelling also.
Abot's Silt Striders, Boats, Gondoliers. All great for adding imersion while travelling.
Regionally Known Criminals. Great for adding some much needed sensibility to the way crime is handled. Based on regional as opposed to island wide notoriety.
Ashlander Tent. Portable home, handy and good for rp.
Children of Morrowind. Add's a lot of atmosphere. Particular favourite is the girl saying. "I went to the temple to pray but forgot what to say so I just stood there and went naaaaarrrrrrrrrrrrr".
Living Cities of Vvardenfell. Put's people and buildings on schedules. Great for atmosphere and believability. Makes being a thief far more interesting also.