Civ IV suffers from some serious problems, but the unchanging formula for addiction saves the day.

I'll try to keep this brief. There are major problems with Civ IV that sometimes make it unplayable. There are known bugs and glitches that have no solution known (as far as I can tell), and support has mainly moved on to Civ V at this point. The biggest problem Civ IV has is with its random generator. It is supposed to make battle outcomes random for example, but this isn't the case. I did a little experiment in one of my games. I was trying to take over an enemy city with three riflemen v one longbowman. The first had a 95% chance to win, the other two over 99%. One was a 99.8% chance to win. All three lost. I reloaded the game, tried again. The same result every single time for ten reloads. Other complaints in forums suggest that Civ V also has issues with its random seed generator that forces players to play the same map or same race every time.

Other than that, not much has changed from Civ III. In fact, just because I never encountered these problems in Civ III, I would highly recommend Civ III over IV. The graphics aren't as nice, but the gameplay is more fluid and makes a lot more sense. The messed up combat and random seed generator really bummed me out on this one, especially since they will not be fixing the issue.