The game received a big graphics update, there will be a lot of eye candy in the environment, and another big change is the introduction of full-motion video of the other leaders, it will be very important to watch the body language of the other leaders to see how they feel about you. Additionally, the game also introduces city states, a new class that doesn't expand beyond their own borders.
If your computer is powerful enough, you'll really see the graphical jump: waves roll lazily across the ocean; horses stomp on the ground and eat grass; military units adjust their gear. It's a living world with new environmentsquareshexes that have different terrain depending on which continent you're viewing. Think: Wide sweeping plains, majestic, snow-capped mountains, dense forests, lakes full of slowly oscillating water, and more. This is why your graphics processor and CPU are going to need a real head of steam.