I am just winding up a Noble game as the Egyptians (Hatty) on a small map with the Mongols (Ghengis), the Incans and the Persians, with aggressive AI and raging barbarians. I was caught by surprise at how much smarter the AI was fighting wars.
The Incans and I managed to pin Ghengis in a peninsula, and I let myself fall behind on military (not by much, but enough) that Ghengis took the opportunity to attack me. He had the only horses and the Incans had the only copper. So when he came at me with his Keshiks, all I had was archers
I sent an additional worker to help the one mining iron to finish quickly, then whipped a spearman at my closest border city. Although he pillaged everything, my borders held, and I brought axe, sword, and spear production online. Suffice to say, we pillaged him right back and he refused to surrender, so we eliminated him.
Partway through the war, the Incans declared on the Persians, who were easily the most backward on the continent. The Persians had joined us as Bhuddists, whilst Ghengis and the Incans were Jewish. So clearly I couldn't let my buddies be overrun (also, if the Incans grabbed the Persian lands, they'd be as like to turn on me quickly, and with more production power than I could counter). So I gave Macemen and Catapult techs to the Persians, who whipped/upgraded just in time to stop a beautiful couple of Incan stacks from taking their capital (as they had my religion, I got to watch the whole thing

)
They eventually declared peace around the time I'd consolidated my Mongol holdings. So I turned on the Incans before anyone could found gunpowder. Boy was I in for a shock.
I opened a two-front war, figuring to take out his flank from two directions. I also had a third group of HAs to pillage.
First difference I noticed was that he didn't turtle in his cities while I pillaged. He sent catas and maces out from his cities to rid his lands of the HAs.
Second, His city resistance was excellent with beautiful groupings of mixed unit types and mixed promotions.
Third, he opened a third front making a direct thrust towards my core. Fortunately, I had the only horses (courtesy of Ghengis' capital) and had roving Knights to chop his groups before they got too far. A second Incan invasion wave hit my core around the same time that my second unit pulled back to support the few (but injured) troops I had left.
Fourth, he had a sortie force of about a dozen mixed units, including catas, mace, axe, sword, longbow and crossbow. Although it wasn't as sizable as the force of mine it met with, my force was spread into about 3 stacks, to minimise collateral damage.
This was when the AI made a mistake. Rather than taking a forested hill near the city I was heading towards (on the other side of a river, and flanking the city - forcing me to take 3 steps around it to get to a non-river side for the city), it tried to fortify on a grassland corn tile the same side of the river as me.
Wiping out the stack slowed my advance, but at that point, he only had the city stacks left to defend, and not enough units for even a sally to slow me down.
So whilst it was a win, the strategic thrusts into my territory, and the tactical use of a sortie force were welcome developments, and actually scared me into thinking I might have bit off more than I could chew!
Looking forward to further developments, Firaxis! Thanks
EW