I never put Morrowind on the same shelf as Fallout and Baldur's Gate; these are very good games, but not because of the plot (what exactly makes it great, I can only guess; probably something very winning).
1) Dialogues
2) Plot
3) The possibility of branching choices in side quests (the main plot is linear)
4) Great opportunities for role-playing.
That's why I think these qualities are the most important for an RPG, because with their help, the best RPG to date was created. Only Knights of the Old Republic 2 can compete with it, after enthusiasts restore ALL the cut/unfinished material. That is, either it will take a very long time, or never. However, the lead developer of Planescape: Torment worked on the dialogues for Knights of the Old Republic 2, so it all makes sense :)
Sieverfail is a veteran, he argued with trolls)
And flies, of course, are attracted to G, so Fallout and everything else is G.
And everything in the world is G, except for Uwe Boll's films.
Where do we end up when we save the world?