Early on in my Skyrim career I wandered out of town towards a bandit camp and saw a big dude next to a gigantic fire. Figuring he might have a quest for me I walked up to him and then he swung his club and me and I died. Not just any death though! The screen showed me rocketing up through the air into the sky, spinning and twitching in my final death throes. It turns out that giants are angry sorts who bash you if you try to go near them. I figured I would try to fight him again and ran up and bashed him in the face with my hammer - after all, he is right beside the starting town so he can't be *that* tough, right? My hammer knocked off 5% of his health and he one shotted me again.
Oh, but I know how to deal with this. When an enemy beats you up you level up and get better gear and then go back and bash their damn face in! I ran from village to village buying ore and soul gems and picking flowers and powered my alchemy to maximum to make potions that improved my enchanting so I could enchant gear to improve my alchemy which made better enchanting potions which made better alchemy gear. Then I capped my smithing and used my maxed out enchanted smithing gear and my maxed out smithing potion and built a hammer made of the heart of a god and tempered it and then it was time to go KILL THAT FUCKING GIANT.
I walked into the giant camp and swung my godhammer at the giant and he fell over dead. His friend walked up behind me and thumped me with a giant club that took off 5% of my health. I spun around and oneshotted that giant too. Then an ancient dragon breathed fire on me as it landed and three gigantic mammoths who were friends of the giants ran in to attack. An ancient dragon and three mammoths simultaneously? Time to drink a "Do double damage" potion! Four swings later every one of the enemies was dead, one attack each.
I may have prepared too much. I knew I was doing more damage than before, but I figured it was something like 5 times as much damage or so since I hadn't paid any attention to just how big the numbers were, only that I had to make them as big as possible. It turns out that originally I was swinging for about 21 damage and now I am swinging for about 4200. So yeah, I am doing 200 times as much damage as before. This would explain why the enemies were melting in ways that made no sense. I am also about 20 times as tough and in addition to that I have endless stacks of healing potions I can use instantly should I be injured so aside from pure laziness there is no realistic scenario where the enemies kill me. I could have easily waded into that camp if it had 30 giants in it and had no problems since the giants can only realistically attack me 2 or 3 at a time.
Obviously the game gets a lot less fun when you one shot ancient dragons and nothing can hurt you so I dialled the difficulty up to Legendary. On that setting I do 25% of normal damage and the enemies do 3 times normal damage and that, it turns out, makes the game interesting again. Dragons are pretty hard, giants are still easy, and I have to drink potions regularly to avoid dying. Seems reasonable. Honestly the simplest way to make Skyrim super challenging is to not craft. Without my ridiculous crafted godhammer and absurd enchants I would be doing about 10% of my current damage and that would avoid the need for Legendary difficulty to have any kind of challenge.