Not as important as how they function, but still important.
People, software programs, buildings, landscapes... appearance is information, about quality, about professionalism, about creativity, about attention to detail.
This is in some other aspects means the opposite
How so? I've played all 3 of those, and much prefer the Civ 5. Or at least I think I do? I haven't played Civ 1 or 2 for 20 years now, so it's hard to compare.
Could someone tell UI designers?
It is deeply troubling how much effort goes into manipulating people, or just pleasing managers who’s checkbox includes “flat design, because?”, and how little effort goes into actually making interfaces visually effortless to understand, features easy to discover, and with flexibility to be really usable from a user’s perspective.
Our bicycles for the mind have become conveyer belts for e-mall shopping.
I don't have hard numbers, but I think flat design really became a lot more popular after Windows 8 was released. For a while, Windows 8 was heavily criticized for its UI design (and not just because it was flat), but they stuck with flat design the entire time, and I believe they had a great role in popularizing it.
I guess we'll just need someone else to make their UIs more realistic and 3D, like the old ones used to be, and stick with it no matter what others say, and the style may become popular again if their UI is in wide use.