This incredible mod restores lots of cut content, including the questlines related to Nerastarel, the Red Queen, the Black Horse Courier, and The Fingers of the Mountain. It can also boast a list of over 50 restored NPCs, with either recovered or AI-synthesized voice lines, new shops and locations, and so much more!
This mod at least doubles the number of things to do and explore in the already rich world, which shows how great Bethesda's ambitions were. Publick Gamer did a tremendous job, which absolutely deserves your attention (and endorsement!)

LINK: https://www.nexusmods.com/oblivion/mods/47191

Another great content restoration mod, which makes the game world more varied. The bottles with potions now differ in color (depending on their buffs), the beta version of the leather armor is now playable, as well as the Mythic Dawn and Palace Watch armor, enemies received new shaders, and so much more!

LINK: https://www.nexusmods.com/oblivion/mods/45909

Spanning over 25 new quests, this mod allows you to experience a story that could rival the in-game guilds! Raise through the ranks, complete the campaign and receive some nice rewards!
The feature of this mod is the appearance of thieves, pickpockets, and assassins in the major cities — for you to arrest!
The hand-picked voice lines provide a relatively smooth experience, so you won't have to listen to AI.

LINK: https://www.nexusmods.com/oblivion/mods/40823

Kvatch is in ruin — and it desperately needs your help! Follow an amazing storyline where your choices matter, help the restoration process, and uncover Kvatch's dark past in a series of horror-like quests. Fight in the arena, enjoy the new architecture, and receive some great bonuses for your devotion!
The mod is almost fully voiced (some lines are missing), but the main characters sound close to the original, which deserves praise.

LINK: https://www.nexusmods.com/oblivion/mods/1541

This mod adds 14 new pets, from pumas to akaviri tigers, from battle boars to skeletons! Feed the animals, play with them, and attend to them when required. The pets will grow with you, getting stronger every 5 levels.

LINK: https://www.nexusmods.com/oblivion/mods/2054

This mod allows you to recruit multiple followers from the vanilla version after successfully completing their quests. In addition to the usual wait/follow, you can ask them to gather ingredients for you, meet at a specific location, or allow them to wander at your place of residence.

LINK: https://www.nexusmods.com/oblivion/mods/48381

Did you ever feel sorry about Menien? This mod allows you to save him!
It works fine with Skyrim Style Vanilla Followers and Kvatch Rebuilt, so you can travel with Menien afterwards or let him continue his career as a guard.

LINK: https://www.nexusmods.com/oblivion/mods/48385

Ever felt like three eye colors for humans and one per beast race is not enough? This mod adds 23 new textures, from different shades of realistic blue to mystic violet.

LINK: https://www.nexusmods.com/oblivion/mods/1838

If you believe the original hairstyles feel a little bit off, this mod is for you! 47 wigs, both male and female, are added to the game. Although not all the hairstyles this mod provides are lore-friendly, most of them look natural. They also come in different colors, so you will certainly find something that suits you!
Please note that the wigs remove your character's ears. They now have to be equipped. On the bright side, the ears adapt to your character's skin color.

LINK: https://www.nexusmods.com/oblivion/mods/40774

This mod adds Vahi's shop in Bruma, where you can buy new clothes that fit seamlessly into the game.

LINK: https://www.nexusmods.com/oblivion/mods/7926

This mod adds dynamic lighting that syncs with the time of day. Finally, you don't have to squint your eyes indoors in the middle of the day!

LINK: https://www.nexusmods.com/oblivion/mods/53298

This mod lights up the windows in the evening. The configurable curtains add up to the coziness.

LINK: https://www.nexusmods.com/oblivion/mods/4955

This mod adds dynamic lamp posts to the main roads of Cyrodiil. Not only do they add the necessary source of light, they also look beautiful! The omod version allows you to modify the lampposts according to your taste.

LINK: https://www.nexusmods.com/oblivion/mods/46131

This mod improves water so that it looks more realistic.

BASE GAME MOD by LprMan: https://www.nexusmods.com/oblivion/mods/8011

SHIVERING ISLES ADDON by halo112358: https://www.nexusmods.com/oblivion/mods/17345

This mod improves the underwater, adding seaweed, shipwrecks, fish, and many other things. Works great with Enhanced Water mod.

LINK: https://www.nexusmods.com/oblivion/mods/6914

Populates the ponds of Cyrodiil with different types of fish. You can also obtain some fillet from them to use in your potions.

LINK: https://www.nexusmods.com/oblivion/mods/30260

This mod adds ducks, swans, and the birds' nests to the waters of Cyrodiil. The nature feels much more alive now!

LINK: https://www.nexusmods.com/oblivion/mods/45275

This mod adds seagulls to the game. Now the walks on the beach are way more pleasant!

LINK: https://www.nexusmods.com/oblivion/mods/52811

This mod adds vultures, robins, owls, and other birds into the game. They can also be caught and equipped instead of shields.

LINK: https://www.nexusmods.com/oblivion/mods/46214

This mod revamps the infamous Horse Armor plugin, providing much wider selection.
LINK: https://www.nexusmods.com/oblivion/mods/46657

Allows certain enemies to spawn even after your character reaches certain levels.

LINK:https://www.nexusmods.com/oblivion/mods/38941

Any levelled item or spell obtained as a quest reward or any unused sigil stone will be automatically replaced by a better version.

LINK: https://www.nexusmods.com/oblivion/mods/39635

Adds the need to eat, drink, and sleep. Fully configurable, supports food from the base game and other mods.

LINK: https://www.nexusmods.com/oblivion/mods/47054