Overall I think it's a very good game, but there are couple of aspects which I still find frustrating, notably:
- Diplomacy - this has been improved through G&K and the fall patch, but I do think there is still room for improvement. I'd like the AI to be more difficult to exploit - it has no problem with shelling out 240 gold for a luxury and then declaring war two turns later - and I'd also like diplomatic relations to better reflect what's really going on in the world: for instance, if I declare war on someone who has attacked a CS I'm protecting, why should I be hit with a warmonger penalty?
- AI aggressiveness - the AI has become much more aggressive since the fall patch and for me at least this was a major step backwards in the development of the game. On King and above it's not really possible to get through the game without being swarmed early on, because the AI invariably decides that it's going to attack you instead of trying to compete with you in other ways. While this fits the profile of many Civs - the Huns, the Mongols, Germany, the Aztecs - it would make the game more interesting and enjoyable if not every AI behaved this way. Ideally I'd like the AI to be more intelligent at higher levels rather than just more powerful because of the free stuff it gets, but I can appreciate that this seems to be beyond the skill of AI programmers at the moment. I also regularly see the AI field armies that it manifestly cannot support, either.
- AI expansion - see above, but I'm less bothered about the AI sometimes getting four cities up by turn 75 than I am by the AI deciding late-game to plonk cities down in the middle of your empire, in lands that are surrounded by your cities but which your borders haven't expanded to fill as yet. Also, the late-game "I MUST BUILD CITIES EVERYWHERE!!!" spam, Sejong's tactic par excellence. Aside from being irritating for the player, it feels unrealistic. I think build cities that cannot be connected to the capital easily or that are a long way away from the capital should come with a sizeable penalty in either running costs or happiness to try and create a disincentive for this. Founding cities a long way from home should be something that you actually have to weigh up as an opportunity cost - is this city ever going to pay for itself, or is it not worth it?