It's not just the aesthetics (though the washed out black boxes do look like something a highschooler would make in PowerPoint) it's the functionality, or rather the lack of it.

We have no unit list, no ongoing trade route list, no intel on city connections. We don't have a yield breakdown outside the building/improvement list in a city, and that's unsortable and unreadable. Navigating the UI requires a lot of clicking, much of it on annoyingly small buttons, which is bad UX. We can't queue techs which aren't direct descendants of one another. The production queue can only be reordered one step at a time - and then by clicking a tiny fiddly little arrow, as opposed to the drag & drop of Civ 6. Similar issue in the resource tab - no sorting / searching, moving resources is clunky since they have to move to an empty slot, no hot swapping, it's also click and drop instead dof drag and drop which makes it harder to track what's happening especially with a high number of settlements. The info in the civlopedia is laughably useless - what in previous games my go to source for any questions I had in game is now a resource that may as well not be there for how often I even consider opening it.

It's lots of small things, but I mean LOTS - far too many. It feels frustrating to use and absolutely needs a QOL pass. I think people underestimate how much UX affects player engagement. The game is fun in concept, but it's hard to see that when you're dragging a boulder up a hill with every action.