Half Life 1 for example. As it did pretty much all of the stuff. Enemys would search for cover, lob grenades in your direction, attack as team etc. No clue about Halo. All I know is that the AI in shooters has not really improved since that day. In many cases it has become even worse. Well actually in most cases. But nevermind. The AI in FEAR1 was pretty decent though. But it might have been also because they usualy hit you hard when ever you are inside a room with more then 4-5 of them and you do not regenerate health while sitting behind a shelf. (not that the game is not throwing health packs over you feet every 5 meters or so, just saying).