New locations and quests
It's a whole new world. Seriously: you can add enough content to Morrowind to keep playing it forever, and the ones we've highlighted here are the best of them.
Bethesda had planned for the entire nation of Morrowind to make it into the game, but focused instead on the island of Vvardenfell to its ultimate benefit. If you dream of exploring the mainland however this mod will let you do it, greatly expanding the map and adding some gorgeous new cities. The quests are a little rudimentary, but mostly you'll just want to explore all this new land.
If you wish Morrowind felt more like Vampire: The Masquerade, then your dream's come true. The Underground is a questline based around a nightclub for the undead hidden in the Balmora sewers, where sexy vampires will send you on quests and one of them can even be romanced. From the moment the club starts blaring songs by The Beastie Boys and Garbage you'll feel a long way from the atmosphere of Morrowind, but it's goofy, gothy fun nonetheless. You'll want additional mods that add a , and if you finish the questline like, oh, infinitely spawning spiders.
The kookiness of The Shivering Isles (a classic Oblivion add-on) has inspired mods for several Elder Scrolls games, and Immersive Madness is the Morrowind equivalent. It lets you join the cult of the Madgod Sheogorath by visiting their shrine south of Molag Mar where you'll find quests to recover an Orc's stolen buttocks, defeat a rock and then a puddle, win a staring contest against a rival cult, and other similarly wacky missions.
Once you've played Morrowind long enough it stops feeling uncanny and becomes familiar. To regain some of that feeling, try the complete overhaul Morrowind Rebirth. Each settlement is recognizable but different, with more houses and NPCs. There's also new equipment, creatures, music, and more. Morrowind Rebirth on its own is enough to make another playthrough worthwhile.
If you got Morrowind from GOG it will already have this selection of plugins made by Bethesda. If not you can grab them from the Nexus, either individually or collected. They include quests to restore the propylon travel network and take an island fortress back from the undead, more armor, arrows, and sounds, and an option to entertain the drinkers at the Eight Plates in Balmora.
Arktwend and Myar Anath
SureAI are a German team you may know for their Oblivion total conversion mod Nehrim, or for Skyrim. Arktwend and Myar Anath were where they started, total conversions that replaced Vvardenfell with a slightly more traditional fantasy world, though one with some gothic touches. They're not as polished as Enderal—you'll get killed by huge mobs of enemies a lot and hear some characters speak German even with the English patches—but they're still impressive achievements.