I guess UI is the thing where they could make big improvements pretty easily. Sure they have made it better over the years, but it still could use a lot of improvement. - The misleading UI when it comes to moving units is probably the most irritating. - Trade UI should allow you to + or - gold/diplo favor in the main screen without extra click. Its should also have options for +1, +10, +100, -1, -10, -100 etc. to make trade easier/faster. Other things: - Recruit Partisans should be made harder and Ai should do it less. It often gets ridiculous. - Constant or repetitive unnecessary messages from other Ai civs. Small thing that irritates me is that when enemy spy removes your governor the UI doesnt show when you get him back like it does when you earn a new promotion.