Initial impressions after just a few hours of play is that the changes to cities make city planning a hell of a lot more important. Not only are cities partially un-stacked, but there's been changes to how population and growth occur, along with improvements to wonders. I don't have many comments on military changes yet, as I've yet to get into any major war, but here is the overview:
- Cities now have districts that must be placed on a map tile. Districts facilitate building certain types of buildings. So, for example, your "main" city tile is the city center, and can build things like walls or a granary. A military district allows barracks, stables, etc. Districts may be adjacent, which will prompt certain bonuses to production, culture, science, or faith, but will remove any improvements on that tile.
- There is now a concept of housing, and it must be at least one count higher than population if you wish your city to grow. This so far has rarely come into play as certain improvements provide housing, many districts provide housing, and even some buildings. We'll see how it goes once I have larger cities and actually get into a war
- There are no "amenities". This is similar to happiness, but on a per-city basis. It makes managing amenities a bit different, but the idea is still very much the same. Not enough amenities? Build a cultural center and then a theater or acquire a luxury resource.
- Wonders are now placed on a tile.
- Moving through rough terrain has been expanded to include things like, an un-upgraded unit must spend a full turn crossing a river. Roads are now a combination of automatically created via trade routes, building certain buildings close enough, and via the military engineer. All of this makes unit movement in game way more dependent on the terrain, and consequently has an impact on city defense.
- You can now send envoys to city-states to help manage relations with them. Their attitude to you doesn't degrade over time (which ended up being one of my biggest criticisms of them in Civ V, as after a certain point it was more cost-effective to just take them over,) but you do have to compete with other civs. Whoever has sent the most envoys (which can be gained in different ways,) is the city-state's "Suzerain" which gives you certain additional benefits like being able to conscript their military for a fee.
All of these changes have made a huge impact on assessing terrain when moving units and building cities. So far, it's been an enjoyable refresh of the Civilization series. I've had to be way more on the ball with planning my city development, and actually pay attention to city-states now. I'll be anxious to see how this plays out late game, and if the concept of a huge sprawling city is manageable or not.
I haven't experienced it yet, but I also hear that Gandhi is still a gigantic dick, as A.I. secondary traits are random, meaning he can be a passive-aggressive nuclear war proponent.