curl-6 on 24 October 2018
Halo Reach stands out for me; not only did different enemies have very different behaviours, but they were very reactive, constantly changing up their tactics in response to how the player behaved. They'd push forward when your shields were offline or if you retreated, flee or take cover when vulnerable, flank your position, etc.
I think the original Halo, Combat Evolved, was the first time I really felt impressed by in-game AI. I still think the enemy AI in that game holds up better than most games today.
