Honestly, it takes a bunch of work. But I'd love to feel AI that uses the cheap ideas players do.
For example, I played a game where I could climb on top of a pillar and shoot down on AI like pot-shots. The AI on the other hand never did this. It's a very uneven idea. The idea that players can creatively use the level or even exploit the level.
Here is the basic idea. You can track player-AI kills. Then track player/environment interaction.
In the case above if we pass 3 cycle of the player climbing the pillar and totally wiping out AI, we allow the AI to see, understand and copy. So each terrain exploit by the player creates a greater change of the AI learning to use the same exploit.

There is also some simple math facts. Like - a ranged weapon travels farther when fired from a height. It does more damage also. I.e. Archers on the ridge.

Furthermore, interaction makes environments fun. -- Was it super smash bro's that I could swim around poles? When we talk environment the question becomes - How can I make both player and AI use everything in the scene like this was a Jacky Chan movie ( But avoid the mechanical issues from other games.)

If?! - I have a group of enemies down hill, and I have a collection of "Red barrels" up hill next to my, why can't I kick them down for a boom?

Here is a real fun one - So the enemy is in a bar - 2 front window - 1 front door - 1 overhanging porch cover/ with 2 v-beams holding it up. So I sneak up to the 2 windows and drop trigger bombs below them. Then I go across the street to the building roof( bar == city). --- Action!-- Through the window I shoot one. Others begin to come outside knowing I shoot from the roof. A few shots to the v-beams and the porch overhang falls and kills them. Now the leftovers try jumping out the windows -- but BOOM and BOOM. I run down street level and jump in one of the windows --- The last are covered behind the bar. I shoot a few bottles then throw a match. Bad-guy barn-fire.

Explore outside of games - every cool game idea was ported from books, tv, and movies.