No armor grades (light, medium, heavy), no armor skills. Just armor. Armor skills discourage mix and matching your armor between their skills, meaning you're at a disadvantage when you wear the armor you find. If you normally wear dwarven armor and you put on a set of glass armor, how are you bad at wearing that armor? It's a quarter of the weight and more protective, and somehow you don't have the "skill" to wear it right? Armor skills are a freaking joke.
If all these stats were applied to every set of armor, you'd have to wear the right armor for the right job. This way there's no "best" overall armor, there's the best armor for the job. Need to hunt for treasure in a volcano? Use the dwarven armor for the heat resistance. Need to fight a lich? Wear the spell resistant Mithril. The factors of every set of armor can be:
Durability
Enchantability
Agility
Speed
Endurance
Climbing
Athletics
Acrobatics
Slashing resistance
Piercing resistance
Blunt resistance
Fluting
Repairability
Frost protection
Fire protection
Lightning protection
Spell resistance
Joint protection
Sound
Shine
Attractiveness
Value
Weight
So as an example, let's apply this list to a standard suit of dark brown cow leather armor, with values of 1-10. The negatives show what stats would be hampered by you wearing this armor.
Weather Durability 4
Enchantability 1 (Can't hold strong enchantments)
Agility -.5 (All armor hampers your agility to some degree)
Speed -.5
Endurance -.5
Climbing -.5
Athletics -.5
Acrobatics -.5
Slashing resistance 2
Piercing resistance 1
Blunt resistance 3
Fluting NA (Fluting is a metal working process to make armor lighter and stronger)
Repairability 10 (Easy to repair and find replacement parts for)
Frost protection 7
Fire protection 4
Lightning protection 4
Spell resistance 1 (Non-elemental spells)
Joint protection 2 (Elbow, armpit, and other joints between main pieces of armor)
Sound .5 (Is fairly silent when using)
Shine 0 (Doesn't reflect light, in regard to stealth)
Attractiveness 2 (Increases with dying or good repair, decreases with wear)
Value 1 (Cheap)
Weight 1 (Lightest armor in the game)
Now with that example, I'll do one more to illustrate. This will be for Dwarven.
Weather Durability 6
Enchantability 7
Agility -6
Speed -4
Endurance -4
Climbing -5
Athletics -4
Acrobatics -6
Slashing resistance 8
Piercing resistance 6
Blunt resistance 5
Fluting NA
Repairability 7 (Harder to repair and find replacement parts for)
Frost protection 2
Fire protection 10
Lightning protection 2
Spell resistance 4
Joint protection 7
Sound 6
Shine 4
Attractiveness 8
Value 8
Weight 5
With the Leather, it barely detracts from your skills and attributes at all while it gives decent elemental protection and basic bodily protection. Dwarven is great for fire protection, joint protection, and is fairly enchantable.
I am almost positive they will return medium armor to the game as it has always been a staple armor until Oblivion, Morrowind and Daggerfall and If memory serves Arena all had medium armor, and with this next being in Skyrim leather with metal reinforcements are medium armors. I would love to see bone armor return as it is my favorite, but that may not be possible as that was a Morrowind specific armor for the most part, so if it does appear it will be in short supply or should be.
Arena and Daggerfall did not have armor skills.