Yeah, I'm not knocking Bethesda for their AI - because it has vastly improved over Oblivion's...
...but Kojima & Company truly are the AI masters.
I dabble in programming, and of course being a gamer, I tend to make games.
Making believable, functioning AI, to me, is not actually all that difficult. Adding things like spotting blood trails, footprints, footsteps, and glimpses of light are very simple things to accomplish, really. Pathing is what I find more difficult to do in a believable fashion. There's only few standard pathing uses in most games (looking at them from a designer point of view); they can just go straight to the player, taking the quickest route to do so; they can follow a pre-determined path; they can move away from the player; or they can simply not move at all. Modern games, because they can do more, tend to more commonly use the set path in addition to the go straight to the player method.
What I think would be cool to see, and unfortunately I can't really think of a way to do it myself, is to have the AI stalk the player. In a game like Skyrim, stealth is a HUGE advantage to the player because he/she is the only person in that world that is able to sneak. Could you imagine playing Skyrim and you're walking through a city minding your business and you turn and see a dark figure quickly dart out of view as you turn. You ignore it, thinking it's just another townsperson who turned the corner. You turn back continuing on your merry way, but unknown to you, that dark figure comes back out of the alley he slipped into and begins to pursue you again, slowly. Every time you turn in his direction, he either darts into a hiding spot or just acts casual. Then, when you least expect it... BAM! He knifes you in the back, whispering, "You've made enemies of the wrong people, boy!" Before you die and have to reload.
Yeah, it might seem like a cheap thing at first; but once you know it's there, you would start to notice the figure and maybe confront him. A simple change of AI like that would make a world of difference in the experience one had in a game such as this.