In fact it depends on the game you want to do !
you can make your own AI.
What lacks in lot of demos FPS made by people here :
the behaviour of ennemies is flat , without any life.
where are the ennemies that can hide , rool on the floor
to try avoid some shoots , or twist their body/head to make you more hard to hit them.
And ennemies that don"t shoot you precisely each time they shoot : ) , ennemies needing reloading or cover !
Some good examples :
Perfect Dark on N64 , Drake fortune on PS3 etc ...
Irs' not complicated to program more life like reactions (with some random behaviour why not)
Even lot of scripted paths/ennemies locations , by using that
sort of beahviour and with some random ones (random positions also) we could have lot better indies FPS