Civ4 to me has one more turn potential - and in fact I have played one single game for over 30 hours of play time. But there is something... missing, for me. Perhaps because it feels like the game has evolved to make my preferred play style - conquest - the least preferred, least addressed facet of the game.
That said, there are a number of truly great changes that are so good you go "why didn't they do that before"? I mean, the biggest might be that unhappy people don't throw your city into total lack of production, just act as a drain on the city. I mean that's been ACHING to be addressed, and it has...
Also, with the problems I've had, perhaps my string is shorter than some for trouble.
The kicker was the border system post conquest. To me, it renders the game not unplayable, but tedious beyond willingness to suffer. Perhaps some changes will take place to capture my interest.
I do see why the original poster feels this, as I feel some of it too, but Civ4 has a number of worthy features that earn it a place with the other games.
Venger