Here are my thoughts on Civilization V:
In a nutshell, it's a lot simpler in many ways, not that it's a bad thing for the most part.
City cultural boundaries now expand only one tile at a time, rather than an entire ring of tiles all at once. Also, if you just can't wait for cultural expansion, you can also purchase tiles, useful if you want to guarantee that a certain resource will be yours (though my habit of doing this tends to occasionally piss off the neighboring civs

).
I also like the Social Policies concept, because now you just add benefits, rather than having to switch from one to the other and go through anarchy for one turn.
Like I said, that fact that it's powered by the Steam gaming system (or whatever it is) means that there are achievements to earn (which has encouraged me to really play this game rather than just the scenarios), such as "Win as each playable civ at least once" and "Build every wonder at least once". Also on Steam, you can purchase downloadable content, such as new civs and scenarios, though I haven't yet gotten around to trying any of them just yet (though I'm definitely interested, once I have the chance).
There are two concepts that I consider to be the real game-changers from the previous Civilization games: City-States, and no more unit-stacking.
City-States are AI civs that consist of only one city. You could either invade them due to being such easy-looking targets, or ally yourself with as many of them as possible since it's the only way to win a Diplomatic Victory.
Removing the ability to stack units (meaning that now you are not allowed to have more than one unit occupy a tile at a time) means that warfare now focuses more on strategy rather than shear numbers. Also, cities are now their own military units, meaning that they can fight back on their own, and have to lose all of their hit-points before they can be captured. In addition, strategic resources are now limited, so you can't make dozens of, say, tanks from just one source of oil. I actually like this new combat system more than what we saw in the earlier games, because now I don't have to keep building so many units and thus neglect improving the cities themselves.
All in all, I'd say Civ V is definitely worth trying out.
