This game started it all, and every addition to the series means hundreds of hours spent conquering the world.
It is spectacular the amount of depth of gameplay that was available in this first game of the series. Much of the diplomacy and economy that is still used in newer games in the series can be found here.
The graphics are typical for such an old game. They opted to use tile units, much like a board game, rather than trying to animate 2d pixel units, and the choice is superb. The game plays much like a board game of Risk might, except it's a billion times more fun (and Risk is pretty fun to begin with). The game is turn based, but in no way does that take away from the action and suspense of watching an enemy army come down on your cities.
The option to choose to play on a map that mirrors the Earth's landscape was brilliant, and probably my most played mode. I also love that the civilization that you choose starts out in the Earth correlate for the are the people are from, rather than a random area. That means that if you want to be undisturbed and allowed to expand rapidly, choosing the Americans would be ideal. If you want to need boats early on, then starting as the English should be your choice as you can only fit one city comfortably in Britain. Picking any ancient empire, the Romans, Greeks, etc, will have you duking it out early in Europe.
The vast amount of complexity in the game is presented in a way that is simple to learn and pick up fast. You also have the ability to automate a lot of the aspects of the game, in case you don't feel like choosing every detail. The AI is spectacular, and choosing which of the many settings is best for you only takes a few games.
The amount of units in the game and their unique stats allow for a lot of strategic choices. The sheer amount of various situations and things you can do is spectacular for such an old game. Overall, Civilization is the cornerstone for one of the greatest series of all times.