This mod edits unique artifacts and/or their enchantments and/or associated spells (and the tempering recipes of the Dragonborn DLC's Dragon Priest Masks) to make them frighteningly powerful, or in some cases to make them not completely useless, while ensuring at least one significant drawback to each, usually just by leaving some values vanilla.
I want my rare, legendary items to be game-changing tide-turners in my war against the hordes generated by ASIS, Higher Level Enemies Hardcore, Deadly Dragons and more, all powered by Combat Evolved. I've been careful not to touch anything that isn't the artifact or its enchantment or associated spells, (or 3 tempering recipes from dragonborn dlc) because I really want it to be compatible with the 184 other .esp files i use.

Ebony Mail, Masque of Clavicus Vile, Necromancer Amulet, Ring of Namira, Savior's Hide, Shield of Ysgramor, Spellbreaker, The White Phial, Auriel's Bow, Staff of Magnus, Volendrung, Ahzidal, Dukaan, Zahkriisos, Ebony Blade and Gauldur Amulet are finished. Skull of Corruption is triple strength, but I haven't added the sweet evil clone spell to it. I've removed the Dragon Priest Masks, except for the dragonborn DLC ones, because i'd rather have improved closefaced helmets working.

*Spoiler alert*
I just finished installing STEP Extended and a bunch of amazing mods to make my game hardcore and brutal. Imagine my disappointment when I got the Skull of Corruption. I murdered a man and stole people's dreams to get this power, and its weaker than my apprentice level destruction spells.
I've tried other artifact overhaul mods, but the balance was never quite right for me. There are some really cool ones out there, but I need to make my own.
Ironically, I haven't gotten around to the Skull of Corruption yet. (*edit* Took a glance at it and it might be more complex than i thought.)
I would prefer to replace the dream-stealing effect with the evil clone power from previous games. If anyone has any idea how to do that, I would love to incorporate that into my mod. Until I learn how to do that, I'll just jack up the power on the Skull and move on.


Presenting:
Better Artifacts! (working title)

I'm going to go through all the Daedric artifacts, Dragon Priest Masks and some other unique artifacts and at least triple their potency. That means the Skull of Corruption should do 150 damage in a wide area when juiced up with dream juice. That is, until someone teaches me how to replace that effect with the original Summon Evil Clone power that we all love.



Masque of Clavicus Vile:

The masque is already pretty good, but I raised the persuasion boost from 10 to 30, increased the weight (very heavy now) and now it can be tempered with Daedric smithing. Its stats are the same as a Daedric Helmet, but much heavier.


Ebony Mail

Boethiah really outdid himself/herself with this powerhouse. Armor stats changed to match Daedric Armor, but much heavier (suffer, mortal!). Can be tempered with Daedric smithing. That Poison Cloak ability does 15 damage/sec instead of 5.


Necromancer Amulet

I love this one. Mannimarco's tool for advanced necromancy has fallen into your hands. Like Callixto said, most people won't recognize the value of it, and 500 is the highest appraisal it'll get, assuming you have a hardcore barter system. I changed the Amulet by editing its description, and completely changed the enchantment on the amulet.
Old Enchantment: Conjuration spells 25% cheaper to cast, Magicka fortified by 50, Health and Stamina Regen reduced by 75%.
Weakness, thy name is Necromancer Amulet.
New Enchantment: My mod restores the Necromancer Amulet to its former lore-based glory.

Conjuration spells are 10% cheaper to cast. Magicka is fortified by 50. Stamina Regen is reduced by 80%. Total Health is reduced by 40 (ouch). Health regeneration is greatly increased.

Not bad, right? A nasty penalty, an underwhelming buff, and an interesting change to PC health. This amulet punishes you for wearing it.


These effects intensify when the PC's Conjuration Skill reaches 75!
Hot dog! This is a fun amulet! At Conjuration 75, the effects of the Necromancer Amulet are:
Conjuration spells are 60% cheaper to cast. Magicka is fortified by 200. Stamina Regen is reduced by 99%. Total Health is reduced by 120 (try not to die!). Health regeneration is cranked way up.

I'm not sure if the Health regen is balanced properly. Future versions may have a different value once I've tooled around with it for a while. I want it to be very fast health regeneration.

These magic effects are hidden in the UI because they made the enchantment's description ultra long and displayed in a tiny, tiny font. I wrote a simple description to replace the one I hid.

WARNING! This amulet can kill you. A Health reduction of 120 could instantly kill some characters. If your character's total health is 120 or lower and you are wearing this amulet, you will drop dead the moment you reach Conjuration skill level 75. I originally included a requirement that the PC's health must be at least 150 for the amulet to activate, but I removed it. Tell me what you think; maybe I'll put it back. I also wanted to include an armor rating boost or an armor spell or something, but I couldn't figure that out.

Extra bonus feature: The Blessing of Arkay will nullify the Necromancer Amulet's power. Arkay won't allow that kind of soul-bending magic. That's why Mannimarco and Arkay don't get along. Too weak to survive wearing the amulet, but love the fashion statement that it makes? Arkay will protect you while you show off at the club! Don't forget to take it off before the blessing fades!


Ring of Namira

One of the lesser Daedric artifacts, the Ring of Namira is fine as is. I raised the duration of Namira's Blessing from 5 to 30 mins.
I added a requirement to the enchantment and to the spell effects: it only works when the PC is not effected by Arkay's Blessing.
Arkay ain't havin' none of this. Don't try to pull one over on the God of Life. He knows about that guy you ate. He still loves you, though, because I don't want to edit the blessing effects in this mod.

When I do make a mod to change blessing effects, Arkay will kill you for owning the Ring of Namira, and all the divines will set you on fire (eternal, unextinguishable fire) if you are a vampire. That's how I had my oblivion game set up.


Savior's Hide

Hircine granted a mysterious pelt to someone who escaped his Hunting Grounds, probably as an afterthought. He didn't expect anyone to survive, and had to improvise a crappy daedric artifact on the spot to reward some poor bloke. Aforementioned bloke then fashioned the pelt into some decent leather-class light armor and had the local wizard enchant it with protection magic.

The Savior's Hide is a good candidate for ability tripling.
Resist Magic 45%
150 points of Resist Poison.
I removed the Ebony smithing keyword for tempering. Its daedric smithing now, baby!
The penalty for wearing The Savior's Hide is that you are wearing an ancient pelt. It smells musty, and it's equivalent to leather armor.


Shield of Ysgramor

Vanilla version is equal to an Orc shield and a little lighter, but cannot be tempered. I'm satisfied. I'll keep the shield vanilla and triple the enchantment on it.
Resist Magic 60%
Fortify Health 60 points


Spellbreaker

My favorite daedric item, it's already the best shield in the world. I put the daedric smithing perk keyword on it and tripled the ward enchantment's potency.


The White Phial

Whichever potion type you choose to fill it with will be endlessly replenished. Thank Julianos that a Master Alchemist is offering to fill it up for me.

"I want to strengthen my magical skills"
Five minutes of Fortify Magicka 80 and fortify magicka regen 5%

"I want to deal more damage in battle"
Five minutes of Fortify One & Two handed weapons 50

"I want to be better hidden in the shadows"
Five minutes of Fortify Sneak and Pickpocket 50

"I want to be tougher in battle"
Five minutes of Fortify Stamina 80 and fortify stamina regen 15%

"I want to resist the forces of magic"
Five minutes of Resist Magic 60

"I'd like it to have the power of healing"
Five minutes of fortify health regen 50% and 100 points of healing


Auriel's Bow

This bow was made by an Aedra's father, who was also himself, or something. Basically, its the token of Anui-El, the karmic antithesis of Sithis.
See: Sithis Antithesis Theory, the Theorhetorically Antithetical Theory of Sithis.

The bow is in the Nordic class, with exceptionally high crit damage. I changed it to Daedric stats, leaving the high crit damage untouched. Added daedric smithing keyword as well. Its faster now, so you can unleash the wrath of heaven on some poor fools. I didn't touch the enchantment or anything else about Auriel's Bow.


Staff of Magnus

A really cool idea, it absorbs magicka at 20/sec until the target is down to 1 point, then begins to absorb health at 20/sec. Interesting and somewhat useful, its mid-range attack has more reach than most other concentration spells.
I increased the Absorb Health effect to 100/sec. If you've drained them of all magicka at 20/sec during the heat of battle, you've earned it.


Volendrung

It weighs a lot more now. Its stupid how heavy it is:43. That's 13 higher than the ebony warhammer, to which this weapon is comparable.
I added the daedric smithing keyword for tempering.
To the enchantment of Absorb Stamina 50, I added Absorb Health 20 and Paralyze 5 seconds. Welcome back, Volendrung.


Ahzidal, Dukaan and Zahkriisos

Dragonborn adds three new dragon priest masks. I tripled the elemental resistence on their enchantments, added Fortify Shout Time 20% and removed their armor rating, armor designation and armor keywords, replacing them with 'clothing head' and 'clothing circlet' keywords.
Now the Mage Armor perk will function while wearing these mage-oriented masks.



I also changed the tempering recipe 'Workbench keyword' to 'NONE'. I am almost sure this will seemlessly remove the option to temper the masks from the game, but I haven't tested that yet. Tempering the masks probably wouldn't work because they have no armor rating or category, so I want to remove the option to temper from the menu. Crap, now i have to add Constructible Objects to the list of things I edited.

I also discovered this mod:
Ahzidal Dukaan Zahkriisos Retexture by Knight780

I think its the only mod that retextures only the dragonborn dlc dragonpriest masks, which was exactly what I needed to compliment either Unique Dragon Priest Masks - HD textures by skyrimaguas or Apophysis Dragon Priest Masks by pondcypress, both of which are neat retexures of the first 9 masks.


Dragon Priest Masks

Removed because they weren't compatible with improved closefaced helmets. Seems like I should be able to make a patch for it, but I don't know how.

For Konahrik, I'm gonna check out this mod
Konahriks Privilege by Edhelsereg

and for Wooden Mask I'll try the main file from this mod and skip the update
Bromjunaar and the Wooden Mask by glemtvapen


Ebony Blade

I raised the weight to uncomfortable levels and slowed the speed way down (its a little faster than a warhammer). Changed reach and stagger to match regular greatswords. It has low damage, no crit damage and can't be tempered; I left those qualities untouched. The Absorb Health enchantment, which grows as you complete the daedric quest, now starts at 2 points and grows to 50 points. Vanilla started and 10 and grew to 30.


Skull of Corruption

It really should have an evil clone spell, but it doesn't. If I ever make another update to this mod, it will be to add an evil clone spell.

I just tripled the magnitude and area of effect for this artifact. Its likely to hit a lot of people now, and it drains 1 dream for every target struck. You'll drain it of dreams much faster now.


Gauldur Amulet

This could've been just another weak artifact in Skyrim, but they just had to make such a big deal about how powerful it is. I had to make this amulet stronger because it was so weak it was immersion-breaking.
It was split into 3 pieces and sealed away, guarded by its draugerfied usurpers. People died to hide it, people died to find it, and apparently a lot of people died because it was used long ago. seems to me that it should boost magicka a whole lot in order to justify such a fuss.

I didn't mess with the fragments, but the united amulet is much stronger.

Fortify Health 60
Fortify Magicka 120
Fortify Stamina 30
Fortify Carry Weight 15

The base value is 10 times higher, and I changed the weight from 0 to 0.5.

Changelog:
v1.0 Finished Ebony Mail, Masque of Clavicus Vile and Necromancer Amulet.
v1.1 Cranked up the health regeneration on Necromancer Amulet to be stronger than Ring of Namira
v1.2 Ring of Namira added
Savior's Hide added
Shield of Ysgramor added
Spellbreaker added
The White Phial added
Auriel's Bow added
Staff of Magnus added
Volendrung added

v1.3 Ahzidal added
Dukaan added
Zahkriisos added

v1.4 Hevnoraak added
Krosis added
Morokei added
Nahkriin added
Otar added
Rahgot added
Vokun added
Volsung added
Ebony Blade added

v2.0 Hevnoraak, Krosis, Morokei, Nahkriin, Otar, Rahgot, Vokun and Volsung removed because I like improved closefaced helmets more.
Skull of Corruption added
The Gauldur Amulet added

v2.1 Adjusted the monetary value of the Necromancer Amulet to match the unidentified amulet from the Blood on the Ice quest. They both have base value of 1000.
Added requirement to the Ring of Namira ability. It now deactiviates when the PC is effected by Arkay's Blessing, just like my Necromancer Amulet does.

v2.2 Fixed The Gauldur Amulet's description and added 15 points fortify carry weight. Multiplied the base value by 10 and changed the weight to 0.5. Also, used TESVEdit to sort masters. Sorry about that.

v2.3 Small typo fixed.
Added Fortify Shout Time 20% to Ahzidal, Dukaan and Zahkriisos.