Scoobes on 10 November 2014
I think the last game where enemy AI was a huge leap forward and beyond anything at the time was the original Half-Life. The enemy AI actually appeared to have tactical awareness (they flanked you, flushed you out with grenades, would hide when numbers were low, move from cover to cover etc.) at a time when most games' AI could barely knew to take cover.
Since then, I've been impressed by the AI in FEAR, Killzone 2, TLoU, Halo and Destiny, but nothing has been as revolutionary as AI in the original Half-Life.
