Having played three or four games with BTS now my personal opinion is that the AI is much more fun to play against. It is behaving more logically and with more cunning, or rather, it has been nicely programmed to appear more logical and cunning (gotta watch those anthropomorphisms!). In a previous life (job) I worked on, and later managed a team, creating expert systems that analysed information presented to them and then, based on captured expert knowledge, advised on optimal strategies for proceeding based on that information. So, the complexity and limitations inherent in creating an AI that works for Civ4 are professionally interesting to me. When considering the AI I try to bear in mind all the factors involved in creating an AI and especially my expectations of what it should be good at and what it is unreasonable to expect is to be good at: Examples of things the AI should be good at: - Efficiency and Micromanagement Every turn in every city the AI can optimize tile usage for current needs. Workers can immediately respond to events and start hooking up newly available resources, upgrade to railroads (though not always prioritizing tiles correctly yet), and fix sabotaged/bombed improvements. - Computing expectations in very specific situations (e.g. estimating likely battle outcomes) Brute force computing should allow the AI to determine the optimal order in which to attack with a stack, where optimal means most likely to win this one engagement. - Staying focused on its chosen path No getting distracted building favourite wonders or forgetting to change production in some cities. Once a path is chosen all cities and units march in sync, (until next turn). Examples of things the AI may struggle with: - Balancing Strategy and Tactics Unfortunately the AIs potential strength in assessing individual (stack vs. stack) tactical combat doesn't always result in good strategy. Optimal tactics in a single battle may result in losses of key strategic units to the detriment of the war as a whole. - Threat Analysis Is that stack a real threat or a feint? Should it be attacked in the field or should my stack turtle in a city? The correct answer may depend on the location of two more stacks that would threaten my city if I sallied. What direction did they come from, where might they be heading? - Overall strategy/the big picture (everything is numbers...no visualization of sweeping strategies) For example...without some pretty sophisticated topographical analysis routines it would be impossible for the AI to accurately compare two borders and assess which is the most defensible and factor that in when choosing which neighbour to attack and which to contain. - Opportunism (often hamstrung by personalities and inability to think strategically) Basically as a human we can assess quickly new opportunities and even when planning war with one nation spot a sudden weakness/opportunity in another area. A peacemonger like Ghandi may ignore poorly defended border cities that most humans (builder or warmonger) would find not just tempting but irresistible. - Vulnerability to, and ignorance of, exploits (If it used them they wouldn't be exploits!) The AI picks from the same hard-coded strategies every game, it doesn't read CivFanatics and try out the new uber strategy of the week, it won't know about that bug in diplomacy that will be noticed in October that allows you to extract more and more gold from Mansa Musa when you renegotiate (fabricated example). Specifically, the AI does not learn from experience. - Adapting (Oh dear, war looked like such a good idea ten turns ago) It decides war with Spain is a good idea and sets about building an army. Meanwhile, Spain builds the statue of zeus, Chichen Itza, upgrades all its archers to longbows and beefs up its defenses in border cities. Now what? Does it still go to war? Does it exercise discretion? Does it delay the war and attempt a troop surge? Of course, this is just a sample of each list, and there are design approaches to allow the AI to deal with each of the deficiencies but never to the same level of competency as a good (let alone master) human player. In order for the AI to have a chance of competing with good players it simply has to maximize the things it is good at and receive bonuses to compensate for its weaknesses. What Mutineer is observing is a synergy between its bonuses and what it has been programmed to do. I personally regard this as a good thing, in an ideal world I would want an equal game for a really good player at around monarch (i.e. 50/50 wins) meaning emperor becomes a real challenge, immortal would be tough and deity almost impossible. In fact as colony just pointed out many bonuses have been scaled back...at 80% on deity the AI will grow an equivalent city with similar tactics to size 10 in the time it takes me to get to size 8, that difference, on the very highest level seems perfectly reasonable especially given the reductions in this and other bonuses (upgradecost%, inflation%, etc) since warlords. How else should the higher difficulties be made challenging? The beauty of Civ4 is that unlike many games where the advantages on higher levels are hard-coded it is very easy to tweak the balance to suit your own tastes. For me personally, on the games I have played so far, Firaxis seem to have done a remarkably good job of maintaining balance despite the far-reaching changes in AI behaviour and capabilities.