Above the usual tropes of having good design, character, specialty and synergy, thought I'd add some [basic] special cases to the mix:

1. Angle of attack: Enemies would be able to come from all 360 degrees, and would not be limited to the ground plane.
2. Player's cone of vision: It would inform the AI where the player is facing, allowing them to have more choices to attack. [This could also lead to changes in player awareness.]
3. Sense of surroundings: Primarily to reduce kiting, but would be useful elsewhere. It would be concentric in design (Close > Mid > Range). Would double as a sensory limit, to call/hear sound cues. [In order to call for reinforcements for example.]
4. Cover/fallback system: Keep ranged units out of harm's way, or get enemies to hide in tall grass to avoid detection. [Or joining up allies in order to survive.]
5. Multiple attack modes: Might have a dagger and a knife, Why not use them? [Maybe both, at the same time? ]
6. Reactive environment: Place traps, loot chests/resources, and take them with them, or to a camp.
7. Player tracking: Either using environmental cues (footsteps in snow), or by player "crumbs" on the floor (if higher level AI). However, these would decay eventually. [Might add aerial tracking/wind direction.] [These also could be used by the player, if ability is available, or would refer to the lesser visual cues.]
8. Different attack tactics: Encirclement, ambush, flank or corner. [Or grab you and try to drag you somewhere else.]
9. Zone/Time awareness: Example: If weak, then would not venture close to an enemy, or would stay more in the shadows. [And come out more during the night; and be more shifty.] [Or would be more active or passive.]
10. Own stamina: YES. Separate from the base aggro-timer.
11. Auto pickup (for player as well): Maybe grab a weapon from the floor or two? [But mostly for the player, to customize their experience; like having auto gold pickup.]
12. More synergy: Mobs would actively seek out tactics, when near each other. [Example: one throws oil on you, the other lights you on fire.]
13. Extra scripted states of behavior: To fill in time between those "cumbersome" moments of having to fight! [Adding more randomness to enemies, by giving them "jobs" to do, like eating, resting, smelling of yellow flowers, etc.]
14. Power sensitivity/Scaling: If player is too low, or too high level, they would either run or be more courageous. [Much like having an XP penalty for doing so.]
15. Reduced predictability: By giving them extra mobility: dash or [trying to] avoid certain attacks, before happening (if smart enough).
16. Whiskers path-finding: To give them more realistic movements.
17. Chance of unpredictability: Enemies might go overdrive, or panic, or grab a random behavior from the pool. [From other monsters, within limits of course.]
18. Intended weaknesses: Afraid of light, or to specific events, etc.

19. Against the elements: Based on their ability to move, and their environment (snow, mud, rain, etc.), their movements would also vary [greatly].