Typically, it takes a lot less horsepower from a console to put out the same level of detail and speed (still you have to knock back resolution given they are meant to play on TVs). The fact a game is coded to run on top of a resource hog called a windowed operating system, and then the code is made to run across a bunch of different architectures, you hardly ever see anything streamlined for your PC.
Still, it sounds like Far Cry definitely has some pretty nice AI. Seems like with each new major game release, somebody goes to the next level when it comes to showing off clever CPU tactics. I'm not sure we'd see the same for something like Halo's enemy AI, as the story might not support stuff like that always coming from the enemy. The Covenant is just not that tight. They have a serious caste system and they only go but so far when it comes to how closely different aliens work with each other. There's got to be some little resentment or division keeping them from working like a perfectly tuned machine.
It's actually interesting in how some games will choose to pursue AI. For instance, Rainbow Six 3 stays somewhat accurrate because of WHO you fight as opposed to simply trying to come up with the most impressive "tight" AI routines. Mainly because you are dealing with terrorist minds and groups of people who aren't quite as organized. They concentrated, instead, on routines that randomize enemy thinking patterns at the start of a mission. Kind of like assigning a "personality" to each person.
Do they fall apart and surrender when a bullet wizzes by?
Are they the crazy 'If I go, surprise them like rambo, I'll take them all down" type?
Are they the 'If I'm going down, I'm taking as many people with me' type?
Are they the 'lose it' type, where they hear something wrong and then they simply shout like a madman and spray the offending area (regardless of seeing the foe or not)?
Are they the Icemen, who are the rarer but 'on their toes' type? (Silent and deadly)
Anyway, the matter is, some games wont pursue the same type of AI because it should only be used for the right kind of teams. When it is believable for them to do so. Far Cry sounds like you face truly organized and professional military squads. Ones, in which, don't fall into the RS3 style of opponent algorithms.