The entire series really peaked with civ 4 and 5. 4 was the more complicated, less streamlined but still really fun game, where each game kind of felt like a dnd campaign where tons of random things could happen and you had a lot of flexibilty with your Civilization. And Civ 5 was streamlined, simplifed to be easier to learn, and while choices were reduced, the more streamlined nature made it easy to jump into a game, and civs still had uniqueness about them, and its also great fun.

Civ 5 is also a beautiful game. The artstyle has this epic, renaissance painting quality, and every world leader looks badass and awesome. Even the portraits of the units, like the worker and scout looked like something out of an italian paimting. The artstyle felt more authentic and mature, at least to me, and they haven't really recaptured that epicness and beauty since.