I finished my first ever game of Civ V over the weekend. It's a shame I never really gave this an adequate amount of time before. Anyway I played with Gods and Kings. I can't really provide a before/after comparison but everyone seems to agree that the expansion makes the game much better.
I played on the easiest difficulty, just to get a bearing on things since V is such a radical departure from previous Civ games. Conquest is particularly different. Whereas with previous Civs city defense was based upon how many units you had fortified in your cities, now each city has a life bar and in a sense handles its own defense. You can still fortify units in town to add to the defense, but cities have the capacity to defend themselves. Capturing a city requires a ton more strategic planning and skill. Since you cannot stack units, you have to carefully plan your distribution of units in order to maximize efficiency. Otherwise you can create choke points that take units 5-6 more turns to get around. You absolutely positively have to come in with a mix of units. At least two siege units are necessary to take down city defenses, along with at least one foot solider. only foot soliders (pikemen, warriors, etc) can capture a city. Siege units, ranged units, etc cannot.
There are more diplomacy options than ever. I can't speak to the AI of other nations. Generally speaking they are dumb and pretty forgiving on the base difficulty.
One quirk I did run into was trying to complete the space ship. You have to construct each part and then move it to your capital city. then you assemble it. Problem is I couldn't make the parts go to my capital city. I ended up having to Google and found my answer: I had an automated worker sitting dormant in the capital, and for whatever reason that forbade my spaceship parts from entering the tile.
I'm still out on the whole hex thing. I know it's probably better for the game, but ehh. I dunno.
