Traps would be fun. Sure, a bunch of level shit kobolds can't hope to kill you in a fair fight.
So you see a chest.
And it whoops! Wooden stakes! A pot of scalding hot water! Some damage and a big debuff and oh-no kobolds!
DDO does a fucking LOT of that, for what it's worth. It's less fun than it sounds when not having a twinked rogue means you can't do a mission, and not being a rogue means you can't solo.
I think every MMO has things it lacks, and people who are more particularized in that particular MMO will probably look for things that are lacking in it. I come from CoH, so I'd say tactical movement. Mobs in that tend to either stay in place, run at you, or run away from you, but there's not much actual positioning. Lining up cone attacks to hit multiple players, getting some high ground and throwing jump suppression on you so they can peg you from range, trying to specifically stay out of melee range, that sort of thing. Things that good players do, especially in PvP, because they're more lateral thinkers than most AIs.
With the addendum that there be something a player can do to deal with anything like that. Respectively, spacing out to avoid AoEs and not just "stand on the opposite side from the tank", there being no space a mob could jump to that can't be reached without jumping (even if it takes longer), ranged effects on melee characters that mitigate what can be done to them from outside melee range, and such.
In CoH, attacks rooted you for the duration of the animation. If you were moving, using an attack stopped you in your tracks. One little oddity was that if you hit an attack while
jumping and moving, you'd keep your momentum until you landed. This meant you could keep attacking the majority of the time while still moving, if you had decent unsuppressed jump speed. Now whatever game you're working on might not have that exact function, but mobs didn't have the AI to take advantage of the fact that the game works that way, and players took advantage of that. If your game has something like that, making your AI able to exploit it to the extent that players can is exactly the sort of thing that should be done.