The best TES moment for me was the Ahdarji’s Heirloom quest where you have to steal the ring off the noblewoman and can do it either waiting until night and sneaking into the castle, or during the day by pickpocketing her in the market, etc.
The added stealth and physics system was such a huge win over Morrowind.
Now in TES6, Imagine a quest like that but with no loading screens or separation between areas, so you could levitate into the castle, or climb up the walls, or shoot a rope up, or use an invisibility potion for easy pickpocketing, or use a powerful Charm spell to make her hand it to you, etc.
And that’s just one quest, with no dungeon-diving or combat!
Imagine drop-in co-op play for dungeon-diving, so you could play with a DnD style party of spellcasters, rogues and warriors. Exploring massive dungeons with traps, physics like Underworld Ascendant had wanted (i.e. burning rope-bridges, freezing water to walk on it, etc.), spells with environmental effects, etc.
Imagine NPCs with dynamic needs, planning and scheduling, and settlements with their own needs and market - relying on traders to exchange goods, and caravans that you could escort or rob. Dynamic enemies like Dwarf Fortress Adventure Mode - bandits and necromancers that take over towns, or infest abandoned settlements and dungeons.