It is true the game was somewhat lackluster in parts, but it had a couple of things going for it. The main two were overworld exploration and freedom.
As I said in my previous posts, Morrowind is still one of the best examples of overworld exploration in the genre. It largely fills the two the checkboxes: There are (1)plenty of things to do and (2)obstacles to surmount.
Regarding the first point, MW offers more than most games: lots of small dungeons, cities, quests, factions, and enemies. Not to mention that due to the unique non-craftable loot placed all across the world, there is all the more incentive to interact with it. It is a vast world, and the game does a fine job of filling it up content-wise. A lot of people don’t like that it feels "lifeless", and confuse that with emptiness while calling it the latter, while they are not the same thing. The game is not empty by any means, the thing is that the content is spread out thinly across a large world. This is a double-edged sword. The disadvantage is that individual units of content feel somewhat featureless, but the are advantages too. For one, there is the epic sense of scale, of a large and deep world out there to be explored and conquered.
Other games try to disguise the fact that they are in fact tiny playgrounds through gimmicks like making overworld areas vaguely dungeon-like(Gothic II comes to mind), but Morrowind goes balls out fleshing out an entire world because it has the content to back it up. That the content is relatively samey(and it is nowhere nearly as bad as games like Daggerfall and Oblivion that try to achieve the same by relying more heavily on procedural elements), is the price for what it aimed to do. People dismiss this factor too often, not realizing that quantity is a quality, and that this is a (legitimate) reason why people keep coming back to this game.
This aspect of the game also synergizes with its commitment to player freedom, because it often means little to simply allow the players to do as they please, if the game does not offer concrete and positive things to do. Morrowind does that, and apart from quantity, it also offers a variety in the things to do that other open world games. The fact that it actually puts a bunch of dungeons inside their overworlds already set them apart from not only the typical open world Ubisoft/rockstar crowd, but even from RPGs that have attempted similar things like Witcher 3 and Gothic 2. It would be missing the point to claim that individually these aspects are inferior to this or that game, since the achievement here is that so many different aspects have been carved into the world, and most of them are done at least decently. Both mechanically and lore-wise, the game is a wonder of worldbuilding. Universality, here as in so many other things, is Morrowind’s virtue.
It should also be noted that Morrowind makes up for the sense of repetition through its wonderful worldbuilding and lore - still one of the very best in RPGs - which makes up to a large extent for the lack of personality of particular people and events by putting them in the context of a world that just oozes character. In Morrowind it is the world and its history that matters, not the individuals in it (it is telling that the most interesting individuals in Morrowind are literally its gods, and embody much of the land’s lore and history). Exploring a vast, deep, overworld like this is one of the few experiences in RPGs that gives you that sense of conquest of the deep unknown that personally reminds me of the feeling you get in strategy games as you clear the fog of war.
As for the second point mentioned above(the world offering obstacles), I already examined it in some detail in my previous posts ITT, though I did come to the recognition that much of its effectiveness is undermined by poor balance. In fact, it is much deeper than that. It could be argued that freedom and options in games are inherently incompatible and always undermine survival elements, and that devs that choose the exploration route will have to choose one or the other down the line. Still, Morrowind did have some substantive survival elements in there, and did as good a job as any game could in offering that as a way to play the game, while also giving the player the option to play the game while exploiting its freedom to the fullest.
The other key aspect of the game is the freedom it gives the player. You can do the main quest, or not, or join a guild, or kill someone and take their house, steal from others, become a vampire or a werewolf, summon daedra, and through the enchating, alchemy, and spell crafting systems you can really play the game like an actual wizard: levitating, teleporting, making yourself invisible, or super-fast, or virtually invincible through spells like sanctuary, reflect and spell absorption. The sheer breadth of options is staggering.
It should be added that a lot of the latter options display a lot of engine interactivity and can also be used to do things in the order that you please and in the process create all sorts of unconventional situations and opportunities for emergent gameplay. This is one of the perks of playing a game that places less emphasis on scripted interactions, and it is one of the advantages that compensates for the loss of "lifelike" characteristics that giving up said scripted interactions results in. It's a fair tradeoff, given the overall design goals of the game. This kind of hands-off approach from the developers often does result in a clusterfuck of bugs, but the fact that the game is largely functional nevertheless is impressive.
People shouldn’t be too dismissive of exploration as a valid aspect of RPG design to focus on, as it should be noted that it was one of the core features, along with character customization, that set RPGs apart from wargames. The reason for this is obvious, a role never exists in a vacuum. Both in the real world and in RPGs, a role implies an ecosystem of which the role is node and a complex of relationships, as much as it is a substantive thing in itself. And the idea of freedom and options, which is also key to the design approach of MW, is also key to RPGs, since being able to interact with the world in different ways results in the ability to play different roles. This concept can be implemented through reactivity and quest design, but also through such seemingly simple things as granting the player the ability to cast spells that allow him to fly around or run like a speedster.