Let's think about it for a moment. What is the greatest computer game of all time?
Answer: Civ II.
When Civ III comes out, what is the worst postion Civ II could be in?
Answer: The second greatest computer game of all time!
Now would someone actaully make the case that they would never again play the second greatest game of all time?
There are several other factors, too. For instance, we can confidently predict the machine and performance requirements of Civ III will exceed those very modest requirements of Civ II. So the machine issue is going to be an issue for many people in the world... not everyone has the latest hardware
. Another issue is platform... I doubt Civ III will be available on MACs or Linux, for instance... at least for some time. In Linux, you'll need WINE or another emulator, which gets right back to the performance issues.
So Civ II will be played, no matter how good/bad Civ III is... 20 years from now, Civ II will still be a great game, just like many people find Asteroids and Pac Man, though dated, are still fun 20 years later!