If you have broadband I'd say try the demo, it gives a good introduction to the game and isn't too hard.
The main difference, I'd say is that it's scenario based rather than having a random epic game like Civ, so there's no exploration or city building. All states are settled at the beginning of the game, so going to war is the only way to expand, normally by picking on smaller neighbours. There's no exploration and no research, you build better miltary units by building city improvements, although you can't physically build every building in every city, there's not enough room and you need to build mines and forestries to exploit resources as well . The main game is turn based, but battles are played out in 3D real time, however you can only give orders to your troops before the battle begins. Diplomacy is carried out by sending diplomats to the state you want to deal with/spy on. Different ethnic groups have different types of troops rather than just one UU (an ethnic group may consist of more than one state).
I thought it was a pretty good game, but it probably doesn't have the unlimited replayabilty of Civ. It will take a long time to go through the different possibilities though, playing the same scenario with different states (you can play any city state on the map) will result in a different experience, as each state will have different victory conditions and you don't have to conquer the entire map.
