The Elder Scrolls III: Morrowind
The bottom line is that it's very hard to enjoy Morrowind without mods, frequent consultation of online wikis, and a considerable investment in and patience for learning it. But when you find your groove you'll have an awe-inspiring, memorable, almost incredible RPG experience. Incredible because there's really no game quite as grand even 20 years later.
Its scope is both broad and deep. It simulates a large and long D&D-like campaign crammed with dungeons, towns, monsters, and intrigue. There are overlapping political story lines with hundreds of named NPCs, many with their own personal stories, and books brimming with lore. There are skill, weapon, magic, and alchemy systems that outdo the complexity of AD&D's Dungeon Master's Guide. And there's an impressively comprehensive UI to manage it all. All of that is packaged in a remarkably open-ended sandbox that engenders many opportunities for emergent gameplay. Go anywhere that interests you and see what happens. It will often be pretty cool and quite dangerous. Many quests offer little direction beyond giving you a goal, leaving a lot of room for creativity and cleverness. And it's impossible to complete them all in a single play-through, as your role-playing choices and sheer coincidence truly do determine your path. You do you.
That said, not all the content is wonderful. There's no dearth of dreary back-and-forth fetch quests that still plague the open-world genre to this day. Indeed, Morrowind giveth with one hand and taketh with the other. Alas, it may very well demand more than it delivers, because it doesn't miss any opportunity to rain on your parade. At times it feels deliberately anti-fun. The most glaring example is dialog: I've never experienced "conversations" with NPCs as tedious as they are here. They are just long, clickable lists of repeated topics with repeated answers. So, immediately a central component of the game is awful. Similarly, journal entries—which are how you keep track of quests—are logged in the order you discovered them and there's no way to search them. Sure, that's how "real" written journals work, but, seriously? In the late game you'll have hundreds of pages of practically unusable text. Online wikis are the reasonable, immersion-breaking workaround. And then there's combat: you can sometimes do the 1st-person dodge-attack dance, but more often than not the outcome of battle depends on the roll of the die and it's a boring clickfest. The Bloodmoon DLC is especially rife with repetitive random encounters.
When it comes down to it, Morrowind plays as if the developers were so focused on the comprehensiveness of their world simulation that they left play-testing as an afterthought. Unless you thoroughly patch it, mod it, and use the debug console, Morrowind is hilariously broken. For example, it's a very common occurrence for NPCs to block you from moving or not being where they're supposed to be. Your only recourse is to load a save or run the "ra" (reset actors) command in the console. And you can easily break a quest line by, say, killing an important NPC by mistake or selling a crucial item to a random merchant. Imagine being 50 hours into the game and having to go back to a save from 20 hours before. You can fix most things with the console, but is that "fun"? It's a miracle that this game passed any quality assurance at all. Oh, and no playtester complained about the unbearable slowness of walking? Really? Without the "Run Faster" mod I would have stopped playing after an hour. The core of the gameplay loop is walking to places. Back and forth. Again and again. A lot.
I did have many memorable emergent moments in my play-through, such as when I knew a powerful companion would betray me and so made sure to weaken him by purposely walking through a dangerous crypt where he would suffer a lot of damage. Then, when he turned on me, he was weak and beatable. That was fun. But, often such moments happened in spite of game design. For example, enemies cannot follow you through level doors. So it's always possible to run away, rest and heal, and head back to the action. It's an anti-immersive mechanic. Multiply this example by one thousand and you'll understand how Morrowind plays. Cheesing is inherent.
And so despite my thumbs up recommendation I suspect that Morrowind is not for you. Its many flaws are, perhaps, fatal. But if you're patient and open to the workarounds then you will be rewarded in spades. It's a masterpiece buried under a mud flow.
Mods I used: OpenMW, Dialogues Decluttered, Run Faster, TrueType Fonts for OpenMW, and Morrowind Enhanced Textures.