I tried to play my first character unmodded, but I just couldn't live with it as it was.

Initially, they were just INI tweaks and texture replacers to spruce up the drab appearance of the landscape. Once Sky UI was released, I couldn't dump the vanilla UI fast enough, and it was all downhill from there. The most game changing mod in my load order atm is probably Midas Magic or SIMS.

Yeah, I wanted to test the unmodded game well. But I couldn't finish the Main Quest. All these mods weren't available then.

I actually think that Vanilla Skyrim is pretty good, it's not perfect though.

If I had the ability to mod I would.

Add a Respec option at the end of the tutorial
Add a better Attribute system
Put in a Weapon/Armor Degration system that's similar to what Kingdoms Of Amalur Reckoning did with Degradtion
Better looking faces although not too over the top
Tweaking the Perk System so that your choices actually matter instead of being cosmetic
New Weapons and Armor that also fits with the lore
Legendary Mudcrabs that can kill you in one hit

I technically play the game in an unmodded sense. 90% of the mods I use are minor tweaks by me, while the rest of armor/clothing. Before there was SkyEdit, and before I used TESSnip'd mods, I played the game for 55 hours. The only time I stopped was because my save file kept getting huge from all the bloat. Eventually a mod was created to deal with the bloat, and I was back to playing.

I couldn't stand the game until I modded it. The characters, stories and everything were fine but the combat, the general easiness of having too much money and being completely overpowered without enchanting/smithing/alchemy made dungeon crawling (80% of the game) extremely tedious and unrewarding.

Now the game is hardcoe and I love it.