Surprised to see so many Far Cry AI dislikes... Sorry to say this but maybe you guys just werent good enough...
FC has the best AI out of all FPS games. They use trees as cover, they crawl walk, they lie down when you shot them with a sniper, they shoot at your last known position. Theyre unpredictable... Sometimes when you hole up in a room they try to enter it while lying down. Other times they enter and start shooting
before they enter haha!
Basically they act the same as you would in their place(in a videogame). They also use vents, a traditional safe spot in games, but not so in FC. They crawl inside and shot you in the ass. I suggest you all play it again on the highest difficulty and see how far you can go... Remember FC mercs are highly trained so stay low and avoid contact if possible.
As for the mutants they were like haunts/zombies from Thief. They added some variety to the mix and they were S C A R Y... Not because of looks(they looked kinda goofy) or sound like in Thief but becasue of the AI behavior. You couldnt deal with them the same as with the mercs. They never went at you in a straight line, they always strafed left and right. Some, like the basic "ape" Trigent had some "traits" i havent seen before or since, like the ability to jump 20 meters in the air. In your standard shooter, when youre on some balcony and the enemy is down then they are
down and they dont go up, unless there are stairs... Not so in FC. First time i saw one(in the treetops) he nearly killed me even though i was in an elevator going up... He jumped and slapped me like a bitch. I still remember the pounding on the elevator floor, below... It was horrifying.