What changes have been made from Civilization 4 to 5?

I've read the surprisingly light Wikipedia article on Civ 5 and it seems to be lacking coherent comparison of features between it and its predecessor. I'm also reluctant to bring down the 4Gb demo on a whim...

Please could I have some clarification on the following:

• Has the speed of conquest been slowed down even further?
• Are wars any easier to end (and avoid re-igniting) diplomatically?
• Are there still culture-related borders?
• Is the AI as aggressive as the article seems to indicate, or is it possible to have stable diplomatic neighbours?
• This one's rather subjective, I'm afraid: With regards to improvements, is this an XP to Vista kind of upgrade, or Vista to 7? By which I mean are they generally look driven, or core gameplay driven improvements?

Let me know if this should be a community wiki, or needs clarification.

Some of these are opinion only, but here's my take on it:

• Has the speed of conquest been slowed down even further?

  It takes longer to capture cities, if that's what you mean, but I think the hex-based, 1UPT, ranged units, and the fact that a unit doesn't necessarily die at the end of each combat (both sides can survive, for example) makes CIV V's combat strictly superior.

• Are wars any easier to end (and avoid re-igniting) diplomatically?

  Kinda speculative; this is difficulty and AI leader personality dependent.

• Are there still culture-related borders?

  Yes.

• Is the AI as aggressive as the article seems to indicate, or is it possible to have stable diplomatic neighbours?

  Again, depends on leader + personality + difficulty level. Stable diplomatic neighbors are possible, however.

• This one's rather subjective, I'm afraid: With regards to improvements, is this an XP to Vista kind of upgrade, or Vista to 7? By which I mean are they generally look driven, or core gameplay driven improvements?

  Personally, I would say Windows XP to Windows 7. Both looks and core gameplay.

Arstechnica has a good writeup on the changes between Civ 4 and Civ 5, and it also talks about the previous Civ's and their expansions:

http://arstechnica.com/gaming/news/2010/09/the-history-of-civilization-20-years-of-wonders.ars

Are there still culture-related borders?

Yes. Borders will expand when your city gains enough culture. However:

• They expand one hex at a time. Which hex you get next is chosen fairly intelligently by the game. You can see which hexes are being considered on the city screen outlined in purple.
• You may also purchase hexes of your choice one at a time with gold. The price varies between hexes between $50-400. (The numbers are a quick estimate, worth researching further.)

The rest of the questions seem subjective to me, although I believe you could reword a couple to be non-subjective.