Morrowind has a terrible combat system and an overly complicated character progression that seems to be complicated for no reason other than wanting to emulate Daggerfall and you can imagine why that'd be a poor decision. It's also stuck in that particular visual hell of early 3D games that tried their hardest at depicting vaguely realistic surroundings only to age about as well as an ice cube in the summer sun of the Sahara desert.
While its story isn't really anything to write home about (oh no there's an evil cult here and they're trying to do evil things and you have to stop them before they do an evil thing!), what is good about it is the way it's structured. Unlike Skyrim, Morrowind straight up tells you during one of the first quests that you cannot do it and that you should go out, do some sidequests and then come back to it. This forces the player to go out and explore the world and learn about it on their own which actually makes it feel like you're exploring a strange new land in which you are as much a stranger as your player character. This, coupled with the fact that the plot is for the most part not urgent and allows you to take your time with sidequests makes the experience feel much more relaxed, when you can walk away from the main plot and return to it after sidequests and not feel this jarring disconnect of being treated like you just came running from the previous storyline quest when you've in reality spent hours picking flowers in the wilderness.
The lack of the typical bethesda "fast travel to anywhere you've already been" system also makes Morrowind feel bigger than many later bethesda titles despite being objectivelly smaller, simply because the player is forced to see more of it. Likewise the world feels more cohesive because the player has to walk to places of interest, with the only way to somewhat bypass this being the Siltstriders which only take you to certain points on the map, mainly settlements and outposts. After that, you're on your own. Having to walk the roads through the length of the game gives the player a level of familiarity with Morrowind that most modern Bethesda games only have for cities and their immediate surroundings. People become familliar with the very land of Morrowind in a non-abstract, "real" way because they know what turns they have to take on roads to get to cities instead of just where the cities are roughly located on a map.
Somewhat tied to this is an entirely personal reason for me, because to me Morrowind feels more like my own adventure because people give me actual directions to places instead of waypoints to follow. One of my favourite parts of Morrowind for me is having to find the elusive Ashlanders since I have to follow signs in the environment and instructions people and lore told me. It can get frustrating but the payoff feels all the sweeter for it.
Likewise, the fact that the world is open but the encounters within it are structured and not adjusted to your level gives you a sense of progression when you return to an area you struggled with before and have no problem clearing it out (apart from the obvious but more on that later). What further enhances this sense of progression is the fast travel system, or rather lack thereof. You start off having to go everywhere either on foot or via siltstrider. By the end of the game, you can fly around. You go from peasant to godlike hero within the span of one game and the progression feels entirely natural and is reinforced by this change that adjusts the very basics of how you play the game.
So Morrowind has all that going for it. But I can never just drop myself into a game of Morrowind and mess around like I can in Skyrim. I have to sit down and have proper sessions with it.
Part of it is the combat. The idea of combat in a 3D, first person space that is based entirely on percentile chances to hit is frankly ludicrous. It is abysmall and apalling and I hate it. It makes combat a chore, a slog that you feel like you have no real input in and as such really inappropriate in a game that is all about your choices and their consequences. Just a series of clicks that you have no input in.
Likewise, the character creator and advancement tools are far too archaic. While they do allow for different builds in some ways they also impair the game and the player in others. For example there's no reason why you wouldn't pick athletics as one of your skills because without it your movement speed will be abysmal. In a game such as Morrowind, where you have to do a lot of walking, not having Athletics will make your early hours a living hell because you'll trudge at a snail's pace until the skill is built up.
A lot of the problems with this are mostly problems of presentation, the game just doesn't do a very good job of telling you what skills do what. And because some skills are essential you will spend long hours just grinding them up to a satisfactory level and your game will be gimped for it.
Finally, the environments. While I lauded them earlier, they also deserve to be criticized because large swathes of them are barren and uninteresting. Most of this has to do with the game's engine and its age, but I still feel they could have worked around that a bit better (maybe say by making the world a bit smaller or leading the roads through more visually interesting locales). It oftentimes feels like the designers bit off more than they could chew with the size and scope of the world.
And that's my thoughts on Morrowind. A very well structured game with a decent story that is severely gimped by some baffling design decisions and overall age.