I was a serious Civ III fanatic for years. Though I haven't played in a few years I'm still a CivFanatic at heart. I've been lurking here occasionally over those years, watching as Civ IV evolved, and wondering when I'd be tempted enough to jump in. It hasn't happened and I now doubt I'll ever buy a copy of Civ IV.
What has most struck me in Civ IV's cycle is the similarity to Civ III's evolution. It seems to me that Firaxis has learned nothing about high quality development. Perhaps it isn't a priority for them to learn, I don't know. I do know that I'm disappointed by their failures in this regard.
Discussions of bugs and patches in these forums have very much paralleled what happened through Civ III's development lifetime. In particular, I think that many people are too ready to forgive and sympathize with Firaxis. My feeling is that people would gain more by setting the bar higher than by forgiving.
It is not difficult to produce higher quality software than I've seen from Firaxis. Looking in from the outside it is easy to see fundamental mistakes (mistakes if one treats quality as a primary objective) in their approach. The biggest example to me is their continuing practice of including new features in patches. For any software team with a high quality mandate this is an absolute no-no. It is common for developers to have "feature-itis" and to remain forever optimistic about their new code. Teams with a high priority on quality learn to offset that with a rigidly self-imposed "if it ain't broke, don't touch it" rule. And note that this very much affects initial release quality as well as patches. A team which feels free to sneak "improvements" into patches is also a team which drives testers crazy during initial development by negating much of their work.
Maybe Firaxis does just as well in terms of economic success, or perhaps even better, by developing what I consider to be low quality software. Maybe it doesn't affect sales much. I don't know.
I hope that Civ V will draw me back in but you can be sure I won't be buying it the day it is released.