Civ II was a toning down of the aggressive AI, but, not too much and opened more avenues of victory besides conquer the world or race to space, although it still pretty much was a wargame as well. Civ II also brought the animated council members that really set it above all the rest in humor and fun just to watch them bicker amongst themselves over what was most important.
Civ III opened up more trading options with the AI, the AI became passive even more and of course there were more options for victory, but, a lot of extra clicking if you played with more than the initial screen of AI players. You'd have to take one out of the picture circle and put another one in and continue to do so for all that weren't on the initial page of the diplomacy screen, this was annoying to say the least. It introduced the General unit where you could attach 3 other units to it and create a stack that could fight as a group instead of singular combat that was the norm for previous Civ versions. Spies were eleminated and diplomats as well. Zones of control were eliminated (two features I hated to see leave) no longer could you build a front of diplomats to prevent to AI from getting to some of your cities before you could retaliate.
Then along comes Civ IV that brings back a bit of all of the versions into one game except for the Council members (cry). There are so many options you can setup the type of game you enjoy from small and fast to epic/huge and 900+ turns. A plethora of victory conditions you can set and a more detailed battle engine that one could create HUGE stacks of armies (not just 3 like in Civ III) and go warring with the other tribes. The AI could be set to several aggression settings as well as the barbarian raiders. Fast settling was toned down quite a bit and made harder so that ole exploit of creating 30+ cities was taken out of the game because the cost and upkeep of them went up with each and everyone you built (though this could be changed back to the old way with a bit of mucking with the XML files). That is the other thing about Civ IV is that the XML files are so easy to use and understand that you can now make CIV IV into the type of game you want to play so easily like my mod which the first 500 turns are in the ancient period and technology advancements very slow. (no tanks in BC period thank god) lol Civ IV also made it where if you got the technology researched all of a sudden you got the resource for it somewhere in your area of control (didn't like this feature much preferred the way it was in CIV III where sometimes you just had to fight for it or go take it) The implementing of religion was fun an enjoyable as well. CIV IV just offers so much and if it had animated talking council members it would be #1 as far as I'm concerned because it can be the "wargame", the "space race", "a diplomacy game", "a culture game" and "a conquer the world game" so much better than all the rest. I'd say it's the best lil "strategy game construction set" out there right now.
