I had an epic series of wars with China in my last game, her tactical AI performed well even though i was deeply entrenched and focused on being a small defensive powerhouse from turn 0. i had the social policy bonus for fighting on home turf, as well as the wonder, so i was a tough nut to crack. It was on an earth map and i was surrounded by liberrated city states and allies. China and I shared just one border, to the south in the mountains around where IRL turkey is (geography fail for not know thier name). there were 4 seperate invasions:
invasion #1: very early modern era, she attacked with riflemen and artillery in a basic land thrust. i counter by introducing the world to a new concept: air power
invasion #2: she learned from he previous attempt and this time brought a contingent of AA guns that kept my bombers in the hangers. by this time i had upgraded 5 rocket artillery that had been defending my nation since they were just wee catapults. I built a railroad parallel to the border, 3 tiles back so they could be moved quickly from one place to place, often setting up and firing in the same turn. the invasion was repulsed.
invasion #3: She apparently recognized the threat my artillery posed. this time, she sent 3 attack helocopters all the way up to the arctic around my allies, they came down and pillaged my only source of aluminum just as a larger land invasion (spearheaded by modern armor this time) reached the mountain passes. Her armor pushed through the weakened bombardment, brushing aside my mechanized infantry and forcing me to pull my valuble artillery back. never before in Civ have i known such a moment of pure panic. i dropped my entire treasury into buying guided missles and shifted production to AA and AT units. thanks to the defensive structures in my southernmost city, and the home-turf fighting bonuses i was just barely able to repel the invasion.
at this point, she decided i was just too hard a nut to crack and started work on her spaceship. I was already working on mine (as had been the plan from the start), but i did not have the production capability of an empire spanning all of africa and asia. only one thing for it, i built a nuclear missile, loaded it in a nuclear sub and sent it towards Bejing. I waited till i could see two parts on the road and one in the city, then pushed The Button.
Invasion #4: She was really pissed this time. I had the entire might of the Chinese empire to deal with, modern armor supported by jet fighters and stealth bombers. luckily i learn too and had my aluminum properly defended this time. I was nearly done with my last SS part, so i put up what defense i could. Somehow i managed to last untill the part was finished and en route to my capital. then, one turn from victory, stupid Siam pops a stupid cultural victory from over in the stupid americas.
that got a little wordy, sorry. but i wanted to illustrate that the AI isn't terrible at war, when they get a decent economy established. i think once the AI learned to mange thier economy better, there will be alot more fun bits like what i just shared.