Potions have a "duration effect", rather than "instant". 

NPC enemies have higher combat AI.

"Follow me. I need your help." is changed to "Follow me, for 3 days..." (you must enforce this "3 day rule" for followers yourself, the dialogue is just for immersion (and reminder)). 

Everything costs more (way more) and you receive way less when selling. Expect to be poor. 

Healing potions don't work while in combat. 

Certain OP perks are disabled (all alchemy, conjuration, and sneak perk trees for example). 

Your carry weight is reduced by 100. 

Health regen is reduced by 80%. 

Magicka regen is reduced by over 97%. 

Healing spells are more costly and/or less powerful. 

Conjuring is more costly and takes 5 seconds to cast. 

Runes and some poisons have actually been BUMPED, as they were useless on vanilla.

NOTE - This was derived from a much more in-depth "hardmode" esp that I have on my own game, but that file has many masters, as it builds off of other mods, like Wildcat, Frostfall, RND, etc... I created this file by copying everything from mine that only relied on vanilla (+DLC) records. I've always wanted to find a way to share my own "hardcore" version of Skyrim with the community, and this will certainly NOT accomplish that goal, but I hope it will be at least a step in that direction. I have not tested this file yet, so please feel free to do so and any feedback is welcome, to not only verify that it is working properly for you, but also any other comments or suggestions are welcome. 
PS - certain aspects (like house pricing) I believe will only take effect on a new character. 

I hope you enjoy.
God bless.
~tcbflash

My other Skyrim mods are...

All Axes Chop Wood
https://www.nexusmods.com/skyrim/mods/110876

Geldis Sells Drinks After 8pm
https://www.nexusmods.com/skyrim/mods/110200

Explosive Gas Trap Reduced Damage
https://www.nexusmods.com/skyrim/mods/110139

Soul Cairn Fix (SIC)
https://www.nexusmods.com/skyrim/mods/110083

Orcish Shield Bashing Damage
https://www.nexusmods.com/skyrim/mods/109873

Crushed Garlic
https://www.nexusmods.com/skyrim/mods/109860

Maces vs Skeletons
https://www.nexusmods.com/skyrim/mods/109777

Axes vs Spriggans
https://www.nexusmods.com/skyrim/mods/109737

Last Resort
https://www.nexusmods.com/skyrim/mods/109372

Slower Regen
https://www.nexusmods.com/skyrim/mods/103496

Exertion
https://www.nexusmods.com/skyrim/mods/109285

Legend of the Ancient Scrolls (a Bible mod)
https://www.nexusmods.com/skyrim/mods/102713

Horses of the Holds and Their Unique Qualities
https://www.nexusmods.com/skyrim/mods/102686

Dawnguard Knight Dagger
https://www.nexusmods.com/skyrim/mods/102066

Bible Load Screens -The REAL Ancient Scrolls
https://www.nexusmods.com/skyrim/mods/101914

Higher Prices
https://www.nexusmods.com/skyrim/mods/101605

Battle Cry Fix LE
https://www.nexusmods.com/skyrim/mods/101584

Oiled Arrows
https://www.nexusmods.com/skyrim/mods/101176

Infused Poisons
https://www.nexusmods.com/skyrim/mods/103324

Weapon Balance Overhaul and Specs Displayed
https://www.nexusmods.com/skyrim/mods/103171

Clear Weather Spell
https://www.nexusmods.com/skyrim/mods/103578