"Has the UI improved enough that you can actually handle large empires without spending six hours a turn?"

Well, yes. I wouldn't say that the interface is perfect, but there are several VERY useful city management tools (Focus on food, Focus on Hammers, Focus on Commerce, Focus on Research, Focus on Specialists, Prevent Growth. All can be active at the same time except the mutually exclusive food/prevent growth settings. Each finds the most optimal pattern for whatever resource you're looking to gain, and keeps moving workers around to maintain that pattern.) to keep things in hand. Also, the city overview screen lets you handle your entire empire from a single screen.

UI.Love++;