The AI conducts war in a more sane fashion. Expect more real-world combat, like sneak attacks and tactical retreats. Even at Prince difficulty, some of the leaders would make decisions that mirrored more what a player would do than what scripting would process. It's not perfect, but it is much more enjoyable. Making the computer retreat back into his own empire after sneak attacking you is a great feeling. On that same token, combat mechanics have become more granular. Instead of 10 hit point units from before, they have been expanded by a factor of 10 to 100 hit points. So instead of a unit dealing 1 damage, it would deal 10 in the new scale. This makes combat more nuanced and a bit more captivating. Sneaking out of battle with 3 hit points left gives you that brow-wiping moment.