I really like the building trees of the Warlock series . While they look slightly janky, I think it's the most fun and informative way to show you what a city can do. For me the UI's strength shines when you open a building tree of a race you have little experience with, as you will immediately start to notice differences in their tree and begin to plan your route to get to certain units, etc. Not saying every 4X game's mechanics would match that style of UI, but it is really cool and I feel it should be ripped off where possible 