I know some of these mods are already mentioned but, i'm gonna make a list that cant go without them:
-Frostfall
-Winter is Coming/Cloaks of Skyrim (compatible with each other and with Frostfall)
-Realistic Needs and Disease's
-Take Notes! - Journal of the Dragonborn (yes, you can write a journal. Cool, right?)
-Realistic Lighting Overhaul (you WILL use torch, OR Candlelight. YOU WILL. YOU MUST)
-Thunderchild (meditate on High Hrothagar, pray to Kyne, respect the Way of the Voice. It adds MANY new shouts, and yes, you can be a Greybeard! you even get their clothes!!)
-Extensible Follower Framework aka. EFF (imo best follower mod in case you wanna make your own Suicide Squad. UFO and AFT are similiar. NOT compatible so dont combine any of these)
-Wet and Cold (I'm not using, and i do not reccomend this one because of its scripts. It refreshes game many times per second and can seriuosly infect your fps. Use only if your PC is strong)
Honorable mentions: Miraak - The Follower. This one gives you option to save Miraak, and make him your follower. It comes with few other stuff that are worth checking out, if your character is interested in saving him at all. The First and The Last Dragonborn venturing together. How cool is that?
Try cooking build and become best chef in Tamriel!! The build is called Gordon Ramsay, i think. It was made by some1 from our forum here, though i cant remember who exacly. Huge kudos for this!