I thought I'd throw in my views on this topic:
The Thirty Years' War is the one I would really love to see. I have not seen any game that simulates that period well at all. I am always in search of games that allows one to simulate history, to get a feel for the difficulties that each side faced--primarily as an education tool.
Heretofore, I have primarily been a Paradox game player, but I am definitely watching the development of this engine closely. I am not one who wants to fight battles and campaigns first--rather, I prefer the diplomacy, where things really happened. Of course, that is probably the hardest thing for an AI to handle. Anyway, that is what I am looking for in a game.