Heh.. If you think FPSC scripts are confusing, go have a peek at some Unrealscript code sometime. Your eyeballs will jump out of your face and run for the door.
It took me a while to get my head around FPI scripts, but now that I've been playing with them I'm really starting to enjoy it and it's actually ridiculously easy. As others have said it boils down to:
If ":condition" is true, do ":action"
The suggestion of making a 4x4 room is solid. I would do that, put an enemy in it, then make a copy of the stock darkai main scripts and then start fiddling around. Also, have a look at Ched's excellent script reference - that thing has become my bible when it comes to this stuff. I literally keep it open on my computer while creating levels, it's become indispensible.
I was able to amp up the aggressive factor really easily by tweaking the scripts that came with Errant's MP53, namely just increasing the distance and chance of AI entities breaking cover to run at the enemy and attack. My AI team mates went from standing around watching me do most of the fighting to charging into battle, kicking baddies in the face before mowing them down in a hail of bullets. I LOL'd the first time one of them did that, I was like "OH SNAP!!".
Dark AI in the hands of someone like Errant who really knows how to script can do some pretty amazing stuff with just a few lines of code. I'm still learning how it all works myself, but I can tell you that the stock scripts that come with FPSC just don't do it justice, and shouldn't be used as a judge of how sophisticated DarkAI really is.