This is quite tough, personally if anyone want tos try out an expansive amount of Skyrim mods I recommend Wabbajack. It allows you to install modlists that are quite expansive and well put together. I used to manually mod my Skyrim back in the day but this is leagues ahead of what I could ever have done.

For singular mods/adds

ENB Boris, the guy in charge of this is a Russian reactionary dude who has some very unkind thoughts about anyone who is not straight. He can be a massive asshole at any and all times. The problem with this is however how brilliant ENB is, anytime you have ever seen a hyper modded great looking Skyrim it's not just the 4k textures doing the heavy lifting. I guarantee it's ENB that really makes it pop out. I really wish Boris would just idk calm down and chill out, but it doesn't seem likely. You can like the work without supporting the artist of course but just keep this in mind about him.

Project AHO Arguably my favourite quest mod for Skyrim, if you liked Morrowind and felt Solstheim wasn't really scratching that itch then you might love this. It really harkens back to old 3rd era Morrowind, the basics of the story is that there is a settlement of House Telvanni, Sedrith Kegran, hidden in Skyrim. You are enslaved and brought there and then begin to work your way up finding out that Sedrith Kegran is attached to a Dwemer ruin with a powerful Dwemer device of some kind powered by Aetherium. I love this mod for many reasons but mainly the setting, story and rewards. This mod is quite kind with what it offers you, which is imo fair because this mod also demands a sacrifice from your character. As a slave you won't be leaving Sedrith Kegran easily any time soon, so it order to justify the lack of freedom and time spent the mod offers great rewards.

Clockwork Another quest mod, I try not to spoil much about this one but the brass tacks is you head through a passage in the Velothi mountains upon reading the note of a treasure hunter/bandit that attacks you. All is not as it seems. Warning whilst this mod is generally quite a normal romp through Skyrim, it demands isolation, no companions, and the first part of the mod can be quite scary. It's the best attempt at horror I've seen in Skyrim to this day and I've played a fair few mods in my time. But honestly give this one a shot, it comes with a great home as a reward at the end.