Problem is that you may consider this game like a game lacking 2 expansions before it can be considered a base game. And 3 more to be at same level or better than Civ4. The question rather is that whether Firaxis and the community thinks it is worthy to put hard work into it in the future. Although chances are low, but not like pigs next week. AI can always be refined both at core level and via scripting. It can be modded as well. That's not that big issue.
AI is the core issue, and explaining why would take a book. Just two examples:
1. The computer never learned to use stacks properly before. In Civ4, all you needed was some espionage to know what they had and where, and then build a stack that would be undefeatable by their available units. Result: owning half the planet by the 2nd century.
In this one they changed from overarching war strategy ("stacks of doom" running rampage) to a tactitcal battle strategy (1UpT). But the core AI is the same --so, since the computer was too dumb to use SoD properly, how can anyone expect it to be smart enough to organize a proper attack in the 1UpT mold? For that you'd need to consider: a) melee front units; b) main force, ranged units; c) fast units right behind; d) reinforcement units to enter as soon as a tile is freed; e) garrison units to remain in conquered land after.
Result: computer *sucks* at tactics, which is to be expected since it already sucked at strategy.
2. Strategic (ergo, military) resources are limited. Which is realistic, since the resources are supposed to be consumed. But it's dumb to implement it when the computer has such a poor AI.
Let's say they have iron and build the max of swordmen: 5. If you trick them into being in bad terms with the civ on the other side of their territory, they'll be exposed on your side. You can backstab them, and get deep into their land before the swordmen are back to defend. By then, they'd be suing for peace (offering you all their cities, but that can be fixed).
So, making something more realistic (something that on paper seems good) does not work due to the limitations on the AI. The civ you attack cannot just build newer swordsmen on your side, and early in the game moving their swordmen to your side is going to take them too long.
All the changes are in that vein. Awesome, if you were playing another human (or a computer with true AI), but miserable when playing the same ol' "intelligent" engine from 10 years ago.
