The Elder Scrolls V: "Skyrim" is an extremely popular game that's been out for over six years now. I bought it in 2011 and have played over 2000 hours of "Skyrim" and "Skyrim" Special Edition. Mods are such a great way to add to the replay-ability of the game and make "Skyrim" worth playing in 2018.
There have been a lot of mod lists by a lot of different people to tell you what they think are the best mods, but these are in my opinion the 4 most fun mods I've come across (keep in mind they may not be the highest rated and many have their flaws which make them a little underrated, but that doesn't mean they're not the most fun). If you haven't played the game before I recommend playing it without mods for a little bit before trying these mods. Also, I will try to avoid spoilers from the mods.
1. Star Wars Mod Collection.
If you're a Star Wars fan you'll absolutely love this mod. Unlike other mods which might add in craft-able lightsabers or some Star Wars armor set you find in a chest somewhere, this mod overhauls the game. The Stormcloaks now where the armor of the rebels from star wars and the Imperial Legion now has Stormtrooper armor.
Lightsabers and Blasters are added to leveled lists which means they appear in the game without having to make them yourself and that NPCs will have them.
Darth Vader is even added to the game and participates in the Civil War. If you use this with other Star Wars mods, it'll create the ultimate Star Wars open world sandbox experience for you in the setting of "Skyrim," especially if you use mods like The Way of The Force, which adds in force powers that progress as you improve your skills, alongside it.
2. Grand Admiral Thrawn: Invasion of "Skyrim."
Continuing with our theme of Star Wars mods, this mod adds in the character Grand Admiral Thrawn from Star Wars. He's been sent to investigate Nirn and was left with many other Chiss (blue people). He and his lackeys wonder around "Skyrim" seeking powerful artifacts and you, the Dragonborn, must stop him.
This is an epic DLC-like mod, which adds in new locations and makes the game very challenging but also very rewarding. The narratives introduced are wonderful and overall it's very fun to kill off the evil Chiss invaders. While there is no voice acting, for anyone who doesn't mind reading subtitles, this mod is wonderful and stands on its own without the help of other Star Wars mods or difficulty mods.
3. Become Jarl of Ivarstead.
This mod is perfect for anyone looking for that RPG power fantasy experience that the vanilla game tries to produce but doesn't deliver on. It allows you to become the Jarl of Ivarstead, which I know goes against the lore but is explained in-game. It lets you expand Ivarstead, adding an arena and other great things.
And you get to engage in the activities of a Jarl, like dealing with bandits, sentencing people who've committed crimes, setting taxes, etc. While a lot of people like the "Become High King of Skyrim" mod (for some reason) this mod is more immersive, rewards you for putting in effort and being a hero, and actually makes you feel like a Jarl while that mod just gave you a palace for existing and never felt like it was special or part of the game.
4. Requiem.
This mod overhauls the game and makes it into a real RPG, where the player's actions matter, anyone can die, and you have to think about the situations you're in. The mod overhauls combat, magic, and makes the game feel more rewarding because things are actually hard, but doable.
There's no health regeneration, you can't be a master of all trades anymore, and perks actually define your character. If you have no perks in heavy armor, don't even think about wearing it. If you have no perks in lockpicking, it's impossible to pick a lock. Why? Your player doesn't know how to! Your race will actually make a difference. You CANNOT run up to Bleak Falls Barrow and take out draugr and a dragon at level one anymore.
If you get surrounded you should probably run. And you can't be an ultimate badass at everything anymore. If you're tired of "Skyrim" and want a different experience, this overhaul will definitely give you one.