The only way that we have to cheat right now is to give the computer player a resource boost at the beginning of the game. As we make improvements to the AI, we are able to reduce that boost. We should be able to remove the resource handicap on all but the hardest difficulty levels. It's a fantastic thing to see the computer attacking with catapults and protecting those catapults with infantry. The unit cooperation is achieved with a hierarchical combat model.
Grouped units have a unit commander that runs the combat for that group.
If a unit runs into trouble, he'll report to his commander for help. If the commander's group needs help, he'll ask the computer player to send more forces over. I think the major differentiations will be the tactics, strategies, and the emphasis on not cheating. To play a game and have the computer build completely different units than the last time and use them in a different way is a great thing to see. Deciding which items are most important and which deserve time is critical.