No, not scripted at all. Read the links. The AI is dynamic. They will take cover, move so they can target you, run away from grenades. There is also flanking behaviour. If you replay the same level, but use a different strategy then the AI will behave differently, there is line of sight calculations and stuff like that, they will go to where you are.
There is an offline bot based gameplay mode where you can have up to 7 bots. This demonstrates a lot of the emergent behaviours.
In a game like Black or Timesplitters, the gameplay is the same everytime you play. It is a memory test, the enemy appear in the same place every time and behave the same way.
There are some great sections in Killzone that deserve repeated playthroughs. This is because of the multiple ways you can tackle them. One of these is a gorge with enemies on both sides. You enter the gorge unseen, but as soon as you open fire the enemy will know you are present. You need to decide which side of the gorge to attack first. If you stand right agaisnt either of the gorge walls you are undercover. You can climb up one side, but not the other. There is a solider with a grenade gun on one side. There are about 12 enemies to take out, they are all present from the beginning of the skirmish. Because ammo is so tight, you cannot just camp undercover and slowly try to pick them off, you have to out think them. Because there are enemies on both sides it is very difficult, you are caught in a cross fire. It probably only takes 2 minutes to complete this skirmish, but it is very intense and fast paced. I have played it over a dozen times and it is never the same, trying to perfect the best strategy. There is a similar skirmish at the end of the docks level where a bridge separates you from 2 elites with heavy weapons and another 2 soliders on the bridge.