Yep, just finished a game.
Pretty good...more complex, but maintains the same sort of feel of the last three. The government/civic choices are more richly complex with religions explicitly folded into it (rather than implicitly), combat's changed a little bit, development's changed significantly ("Whadda ya mean, my railroads don't increase production now? No income for roads?") The research tree seems, if anything, somewhat dumbed-down.
Overall, it's a creditable successor. III's still my favorite, though.