I've found AI's like Alexander are very good at breaking other AI's now, I can almost rely on Alexander making another AI his b*tch.
It is still possible to use counter-armies very effectively against the AI, they can be very predictable and will do things like mass horse archers, which is totally dominated by Elephants. Also if you are agg or cha against a metal-happy AI shock axemen will tend to make a real mess. In one game I ambushed and killed 15 of Ragnar's units in a row with no losses, getting loads of exp in my units. However later he returned with a vengeance and parked a whole lot of trebs with a healthly elephant, crossbow and more escort on a hill next to one of my flatland cities. Foolishly I tried to hold the city but his masses of trebs easily broke the city. I can say for certain that trying to defend a non-hill city against an AI stack of doom is folly, you either defend a hill city or destroy the AI stack on flat land.
The very newest version absolutely adores promoting Axemen with Shock* which makes Agg AI's a real headache, shock axemen with some spears and swords escorts are very hard to counter until Catapults or Crossbows and even with those superior units they can win through sheer numbers. I'm certainly finding it nearly essential to be Agg or Cha to get a promotion edge/equality on the warmonger AI's and it's simply not worth founding off of hills if you're going to be fighting, unless you have ivory for open-land domination.
* I wrote some promotion code so the AI better chooses counter promotions. Basically it will be very reluctant to promote contrary to an existing anti-type bonus, for example spearmen with their +100% vs formation will mean that any promotion which *isn't* anti mounted will be unlikely to be chosen, meaning the spearman will tend to go with Combat until Formation.
Units like Knights or Cavalry with no anti-type bonus will tend to promote to counter their own kind, meaning in this case combat and formation. The magnitude does matter here, Riflemen for example with their +25% vs Mounted, that is not enough to "Drown out" the desire to pick Pinch to counter own-kind units, as such Riflemen will tend to be promoted with either Pinch or Formation, with neither totally dominating the other (and it's heavily discouraged from picking two different +25% bonuses on the same unit, instead sticking with more combat to properly specialize the unit).
When you have units which counter their own kind already, like Axemen (melee with anti-melee bonus), both trends work together to pretty much guarantee Shock Axemen, the same with Pinch Infantry.
This promotion scheme means the AI can mass up some very nasty and hard to counter units. While the human can still choose better counter-promotions contextually, the AI does at least do decently heuristically and the stacking of counter-promotions means the AI stacks are harder to attack - your units are pretty much guaranteed to come up against some nasty piece of work like a Shock Crossbow or Formation Elephant, and trust me that jabbering hordes of Aztec Shock Axemen means a miserable day for a player stuck with only metal units for defense
.
