I agree with a lot of these. And since I've referenced Alpha Centauri umpteen times so far, I'll do it again!
1. In AC, the AI would quickly turn against you. If you were first in ranking and an AI second, the AI would hate you. Even as an ally, the AI would screw you behind your back. Heck, I remember being extremely technologically advanced...I gave a tech to my ally, number two. A few turns later, that tech (hovertanks, an end-game unit) was beginning to show up in my current enemy's armies. Furthermore, if you were WAY ahead as a player, the AI would all sneakily work against you. It was a very nice thing to have happen, actually...it was humanlike. The better I got, the more irritated the AI got, to the point that I actually lost some of my not-so-close allies. Likewise, my 'tight' allies, who were totally satisfied with me, loved me even more.
2. Even on lower difficulties, the AI acted and reacted according to its...type. For example, there's the Hive, lead by Yang. The Hive were warlike, and they had powerful innate defenses. They shared a landbridged with me into my territory, and went to war with me. One of their allies also went to war with me. Now, I was faced with a quandry: I had Yang's armies (which were, for the lowest difficulty, fairly large) approaching from the south, and his ally (on his other side; unreachable by me) was reinforcing his cities.
So! I pressed into Yang's territory, captured a city, only to be forced back within two turns. Suddenly, my decent-sized army had taken heavy damage and was forced out of Yang's territory, and I had Yang and his ally approaching the landbridge. I moved most of my troops there, and fought back waves from Yang as his ally actually set up artillery and bombed the crap out of my highly advanced army. It took me several dozen turns (literally) to finally build up anti-artillery bunkers and get a whole city up and running just to hold Yang back. It took me an eternity more to press into his territory. Ultimately, the war ended in an uneasy truce and lots of shadow warfare between us.
THAT was a fun game. And the AI was at its lowest. At its lowest, I still had fun in those games. And I have never finished a game of Sins, a game of GalCiv2, or a game of Age of Wonders: Shadow Magic. But I have finished MANY games of Alpha Centauri.
What's the point? Yang had numerous but weak units; his ally had decent defensive units and artillery. So Yang fought with his soldiers, his friend with ranged units, and I had to bring in most of my navy to bomb the landbridge mercilessly to gain an edge. Events like that made the game fun, because even a weak faction could become a huge pain in the rear just because of sheer tenacity. Not to mention that Yang didn't just represent another random conflict, but actually made me think tactically (if I lost the landbridge, I would have lost a whole lot of territory to Yang).
As to their types? Those who went to war...went to war. Those who favored their economies went to war very rarely. Peacelovers...went to war a lot, actually. Scientists kept locked in their ivory towers studying powerful techs, and when war came they produced - not just normal units - but special ops teams that didn't fight by conventional means. Along with some normal units!
If Elemental can replicate games like that, with factions acted in unison and fighting tooth and nail for what they want, I'll be happy. Heck, it got to the point where certain factions would act in one way or another and I would actively come to hate them (Sister Miriam, I am looking at you) or have a strong desire to ally with them (isolationist Spartans, the nature-worshippers, the techies, etc.) because of what they offered. I was strong in tech and population - they offered beautiful compliments to my own forces.
And now, I have a strong desire to play AC again.