This game is the best way to waste your time. I mean that in a good way. I spent days and weeks and months with this game. It's beautifullly thought out, highly challenging, educative in parts and a lot of fun. It's also relaxing and despite it's flaws the best strategy game I ever came across. The expansion packs add some more fun, especially in the later parts of the game and some more variety in the earlier parts: They integrate corporate structures in your empire or state, emphasize religion and culture a bit more and add new leaders and civilizations to play.
Despite all this praise, years of playing this gem allow for some critique. There are some rather annoying flaws in the game. First of all, balance is an issue. You can tweak your random szenarios a bit to make the game more fair. But some civilizations still tend to be more powerful that others. And all will fail when confronted with a bad starting location or bad luck with random events. These - like everything else in the game that's based on chance - tend to affect the game greatly in the beginning and to become mere trifles towards the end. Also, the game becomes almost impossible to win on higher difficulty levels. While it will still be fun to play, you will end up on the loosing end more often than not. Also, combat can become weird with units stacked on top of each other. Often, you will do fine until one of your friends decides to wipe you out with the majority of his units stacked into one army. That will also be your best chance of winning, making other strategies obsolete at times. Other flaws are in the science tree and in diplomacy: The science tree is ludicrous if you look at it closely. Diplomacy is very underdeveloped, with threats or advances for help from rivaling civilizations becoming repetative and annoying.
Nonetheless, the game was better than anything on the market when it came out and still shines today. With the following titles of the series not adding much to the concept, it is probably the best title in the whole series - and one that still runs smoothly on older machines.