I would say the civs, their abilities, and their leaders are on the whole better researched. The policy cards and governments are more detailed and nuanced than previous games' government systems (the problem of certain cards simply being better than others in all circumstances being a separate problem of game design, but the idea at any rate is good). Unique Great People has given the opportunity to showcase individuals who did not lead a civ and who are not just names on a generic Great Person (so it actually makes a difference whether your Great Scientist is Hildegard von Bingen or Isaac Newton, for example, beyond just an arbitrary name). Immaculate research was done for the musical themes for each civ, with most civs having themes based on folk songs and using civ-appropriate instruments (including a reproduction of a Mesopotamian golden lyre for Babylon's theme and a carnyx for Gaul's). City lists are still a mess, though, but hey, at least that's an easy fix for mods. Just a few things that come to mind off the top of my head. As for the art style, I think it's just a matter of taste. I think Civ6 looks great (mostly) and Civ5 may be the most hideous game I've ever played, but many people feel the opposite and that's fine, too.