Hireling/Pet A.I. isn't; intelligent that is. There are some significant issues with it.
When hirelings/pets are set to Active (they will actively defend you and attack hostile monsters):
1) they will stand there and do nothing while I am being beaten to death. This includes my cleric not casting heals on me
2) a hostile will be charging towards me and the hireling/pet will ignore that one but go after a monster way over there who isn't even bothering us
3) the hireling/pet will spot a monster (not being hostile towards me) who is clear across the dungeon, behind who knows how many walls and doors. I certainly can't see it, but they can. They go running through the entire dungeon to get it. But after a point, they decide they are too far away from me and come running back; with a large army of now hostile monsters in tow
4) the hireling/pet will go after a non-hostile/hostile monster within visual range, get right up to it, stop (not attack), then run back to me. When they get back to me, they run back to the hostile, not attack it and come back; back and forth, back and forth
5) hostiles will be attacking the hireling/pet and the hireling/pet will just stand there, slowly dieing, doing nothing to defend themselves
6) hireling/pets will not attack the monster I am fighting even when I use their action bar to specifically command them to attack.
Other behavioural problems I have observed:
1) they refuse to walk through some doorways; they have to be summoned
2) the stand in traps allowing themselves to die; too stupid to move away from it
3) refuse to respond to issued commands no matter how much you click their action bars; you have to summon them then they will answer
4) they will walk to a lever I've commanded them to interact with, then come back claiming it's out of range
5) they will walk to the wrong side of the door, then complain the lever is out of range
6) they will claim the lever is blocked even though there is absolutely nothing between themselves and the lever
7) pathing problems in general; the new animated scarecrow is the worst one. The scarecrow will fall behind because there's a little rock in the middle of the road and he can't figure out how to get around it.
All of these issues should be fixable. The lack of hireling/pet A.I. is one of my biggest frustrations with a game I otherwise enjoy playing. In certain situations, it renders the hireling or pet pretty much useless and I wonder why I bother summoning them in the first place.
If it matters, this is using the Mac client.