Just some more comments on the AI having played some more games. The AI doesn't tend to buy more expensive or higher defence units even when they clearly have a lot of resources. So- I have played games when the AI have thrown waves of relatively cheap and weaker units which I have countered by using Ogres (one of my favourites- only 10 to buy and really tough). If you stack a load of ogres with a hero and some magic upgrades on a castle you are basically invincible. The AI also doesn't seem to buy any additional heroes and can be very rash in the early game with their heroes throwing them into risky battles and losing them and then not replacing them. I have also seen very strong AI players leave their home castle with little or no troops on them so that in one game when I was on the ropes and the AI had 4-5 castles I was able to sneak a force round the back and into their home castle and game over which felt a little like a cheat. Perhaps if you lose your home castle but you have another on the map your "capital" should be transferred to one of the others (or make it an option)?