1. Flanking/baiting type behavior
2. Medium wind up, unblockable, extremely high damage attacks to punish turtling behind a shield
3. Some form of leashing behavior, to prevent enemy groups from being cut down one by one, and to counter perching behavior
4. Basic, high damage counter attacks to prevent mindless melee spam
5. Some basic enemy party dynamics, like mage enemies buffing and healing their allies, high health enemies trying to distract and block the player from hurting weaker enemies, etc
6. Some basic hate prioritization beyond attacking whoever has the highest health
7. npc usage of racial powers
8. Counter spells, spell absorbtion/redirection abilities
Would love to have these.
Yes, I would like it if Skyrim were as challenging as Demon's Souls (haven't played Dark Souls yet) but I wouldn't want the same gameplay. I hate replaying the same stuff over and over again. It's immersion-killing and always seems like it's being done to artificially stretch the length of the game. If the combat in Skyrim were as difficult (though less predictable) as Demon's Souls but kept Skyrim's save anywhere system, I'd be happy.
More importantly, I'd only want Master difficulty to be this challenging. I think Adept difficulty is fine for most people and it would be dumb to change it. That's why we have difficulty sliders.