New and updated features of Civilization 4
Here's a short and incomplete list of new features in Civilization 4:
Wild animals were added to make exploration and expanding more dangerous.
Barbarian tribes are now far less helpless.
Great Leaders are gone, but Great People were added.
Sing praises to Firaxis, corruption and waste are now removed.
Now you can trade food.
Religion. Meet the new concept in the game.
Artillery made more powerful and now it does damage to all units in a stack.
Supposed to eliminate 'doom stack' approach.
You'll need to spread your troops to evade bombarding.
Units now can't grow within usual regular-veteran-elite scale.
HMM style unit promotions were added.
No military leaders from civ3 now available, but Great People were added.
No eras in tech research.
Several Golden Ages can now happen during the same game.
Firaxis promises a smarter and less cheating AI.