I thought HALO had good AI, and there was a writeup somewhere (IDK where) by Bungie devs about how they implemented complex seeming behaviour with some relatively simple/dumb rules.
Within the context of a game it [generally] doesn't need to be a full blown AI solution.
Combining route finding, goals & priorities, situational awareness, and also adding in some flakiness so it's not perfect can give a really good and usable approximation to AI from the human players perspective.
The computer player needs to have rules and knowledge in place about the game such as how to get around the maps and how to shoot / evade the enemy all without being too good.
Dumb was really a poor choice of words, I basically wanted to say that the rules were incredibly simple and even so you get this complex behavior that comes out of it.
I remember the first time I played HALO and the guys talked to each other, and it wasn't just random sound effects they actually did the thing they were talking about. If the Elite guy said to "flank him" they would try to flank you or whatever, it was very cool.
