I feel like there's something I might be missing, but from what I've seen, most of the unique improvements in the game seem complete crap. I'm talking about stuff like the Sphinx (1 faith, 1 culture), the Ziggurat (2 science, 0-1 culture), the Mission (1 faith, 0-1 science) and the Chateau (1 gold, 1 culture). Why would I ever want to waste a builder charge to build these improvements in the very early game, where their yields could actually make a difference, and what are the odds of actually wanting to work these tiles? I loved the unique improvements in Civ5, because they were very powerful and gave each civ a unique twist to their gameplay, but in Civ6, it seems that I will go through an entire game without ever building one of them other than just to try it out. The exception from this rule is India's Stepwell, which seems amazing.