After finally being allowed to play the full version -- don't do that again, Firaxis -- the difference between Civ V and Civ IV becomes rather obvious: Civ V is about evolutionary, organic growth, while Civ IV let you change things in leaps and bounds. In the new game, you build your buildings and choose your social policies, and the immediate effect is small, but down the line, it becomes frightfully important. It's sort of like gardening that way. Don't chit your potatoes and you'll be unhappy two months later. Or, for a more fitting example, we're comparing the histories of the USA and Germany. Civ V is like America: You write a constitution in the late 18th century, and then you change a little here, amend stuff there, and 200 years later you end up with something very different. But it happens slowly. Civ IV was more like Germany: You start with a country in 1871 and -- wham! -- you go through a monarchy, two democracies, fascism, and communism in (relatively) quick succession. Personally, I like this new form of growth. It does require a completely different kind of thinking and strategy, which is probably why a lot of people don't like it. Personally, I like it. But I also grow potatoes.