Eurogamer: When Civilization IV came out - and I'm using the z spelling with the same counter-intuitive courtesy that allows me to refer to drag acts using "she" - it was difficult to say, "Hey! Everyone! This is the big new thing that makes Civ IV the one game in the series that'll make you guff up your lungs, in a way none of the others previously did!"
There was religion, but Civ's a balanced and even-handed affair, so religions were slotted neatly into the tech tree. Moreover, like political systems, each one was a viable gameplay option. And not, as a petty-minded athiest like me was hoping for, an inexorable mental journey from storm-worship to rocket-fuelled godlessness.