^The only problem I had with the religion aspect of Civ IV was when your missionary would fail...in one of your own cities. I get that that sort of thing would certainly happen in real life (kinda,) but it's just one of those things that makes me want to pull my hair out for some reason. It was especially annoying in the late-game when you have free religion and want every city to have as many religions as possible for more happiness, more temples, more culture, etc. "Missionary Failed." NOOOOOOOOOO!