Another great feature you do not see in MMOs anymore are cursed items. In Meridian 59, about 10% of all magic items were cursed.
One famous one was a Ring of Asphyxiation. You might come across a Ring of Invisibility, put it on and instead of vanishing, you start to choke to death. After a very short period of time you life would drop down to 1 HP. Only way to get it off was the Remove Curse spell.
Cursed items also came in a variety of ways.
You might get an item that actually works but has a negative effect. ie. Sword of Flames does 10 extra points damage, but unknowingly to you, if you critically hit or miss it explodes doing 100 points to everything in a 10 foot circle, including you!
You might get a chest piece that makes you immune to fear effects, but whenever in combat you lose 25% of your armor defense.
There can be many varieties to curses, which is why they can be so much fun.
Anyway, do you think they would be good for ESO?