I must say i was impressed in my last game on 7th level ( played as Bismarck on world big map with 22 civs - original start ). Let me tell you in a short. It was a year 1785 and me and Russia were having a big fight which is now 600-700 years!!. Through this time i was able to conquer only 1 russian city. I was very aggressive ( too much i guess) so i was quickly denounced and declared by everybody ( war with 22 nations and located in the middle of Europe..hmm). Still i was able to hold every city with little loses however russian front was something special. Moscow was my main target, but somehow i was unable to conquer it. They were always 4-5 techs in front of me ( i have no money to research deals to make my progress, still must build units to defend which hurt my economy) which means better weapons ( catapults against cannons, more mature units, for instance russian cannon has 3 ranged deadly attack which completely wipe my unit in woods!).
In last 100 years ( it is 1890 now) war with Russia was still on with short peace period in the middle, lasted of course no more than 10 turns as they declared again. I was finally able to conquer Moscow ( after 400 years!! ) with a lot of casualties, but this goes due to the fact that they were attacked by China, Siam and Mongolia from the west. My focus at this time were dropped a little regarding war units ( Moscow was captured and there were no russian cities near which would be necessary to get) so i oriented more to the economy and science to be able to catch the leaders or at least be able to fight evenly when the time come. I naively believe the data from the statistics and information drop menu that Russia losing the war in the west and will be occupied in the west front, but tough luck - they called a truce with them. At that time ( must have some research agreements or Sid Meier there) because they researched infantry, flying and artillery and deployed quite some numbers of modern units in our border.
Point of all this is the AI behavior in the attack ( specially latest one - they used air units to soften my exposed units in hills surrounding the Moscow, then they attacked with infantry using anti-air units in the middle to defend their artillery in the back. Still artillery was little quit and not used as it should and a noticed numerous fresh anti air units ( possible upgrades?). Nevertheless this game was so great with this battle between Russia and us that i even stopped to pay attention to leaders, scoreboard and finally win was not my primary goal anymore.
The waiting turn time was less than a minute ( 1890), so game was still very enjoyable, but the difference here was an AI attack moves which were quite impressive ( at least for me) and must say i never noticed this kind of AI behavior before.
BTW the game is still not finished, currently i am in 6-7 place regarding the statistics ( UN were build, Apollo program started, nuclear bombs are near, but hey - who cares, i will first try to defend from the Russians and then i will go for counterattack - if game will be won by some other AI - nice, my aim is now not to win the game but to defeat the russians..)) For me this game is main reason why i will stay active and support devs to make this game even more enjoyable.