BtS is a much larger expansion on Civ4 than Warlords, IMHO. As mentioned, and as most of you know already, espionage is a huge addition and a critical component of BtS. Before I got the expansion, I was thinking that Corporations would also be a huge component, but IMHO, they are not nearly as crucial to the game, nor do they play a huge role in your strategy until late in the game, when you should be about to win or cursing yourself for not winning already. 1) I have already played several games into the late middle ages, and I actually played one to a diplomatic victory for 70k points on a large Terra Map as the Dutch, where I was a heartbeat away from a domination victory. (I'm sure others have accomplished more already.) 2) What I've seen is that you have to set your espionage to 10% of your economy ASAP and try to stay ahead of the AI in terms of their EPs vs. yours. (EP = Espionage Points, which are what your spy requires to perform various missions, the more complex/valuable the mission, the more costly it is in EP, and if you have more EPs invested in your oponent then they have invested in you, the cost is proportionately less.) 3) Espionage has far ranging capabilities, from allowing you to share the line of sight of the cities, to knowing what their cities are producing, to causing revolts, influencing the state religion, and other ways of reaking havoc, including stealing technologies! 4) IMHO, the costs of mounting espionage and counter espionage campaigns far increases the value of the financial trait, let alone the increased maintenance factors already in place for BtS. 5) The Apostollic pallace...Second to the influence of espionage, I cannot say enough of the impact of spreading your religion in combination with building and running the Apostollic Palace early in the game. 6) The Tech tree...it has been revamped in a couple key areas, mostly in the transition areas between ancient era and classical and medieval and industrial and industrial and modern. New units also, but nothing too major, except it mittigates some of the human player's advantage in terms of going for some unballancing sling shots, making it harder to get a significant military advantage (not a bad thing, mind you, but I note that your mod also does this, so you'll have to investigate how your designs might possibly become too taxing in terms of realism and ballancing the human player's advantage vs. the AI.) 7) The AI...it's just better. Yes, it's true that it's easier to whipe out your close neighbors, since the AI doesn't cheat anymore, but the ones that are not immediately nearby grow stronger than ever before. Additionally, the economic impact of hyper-expansion early in the game is significantly negative, a fact that is exaccerbated by the influence of espionage in the game. In short, allot of the balancing concepts that people have been discussing since Civ 4 vanilla came out appear to have finally been implemented. In conclusion: I'd say your greatest challenge will be how to incorporate espionage and the new tech tree against the environment of an enhanced AI. If you were to just straight up apply your mod to BtS, I think it would be exceedingly difficult to find the same balance of reality and fun as what is currently in your mod. My 2 points of commerce.