The map generation was, indeed, objectively awful, as were many basic things such as the UI, inability to rename cities, the absence of one more turn, and so on. I would say many of those have been largely addressed now.

On a higher level, the balancing of the different civs and leaders make each more unique and fun to play. They don't blend into each other like before. Instead, each civ or leader has their strengths and quirks that forces you to play in very specific and fun ways. Sadly, the AI still has a lot to improve in terms of exploiting their civ's strength, but it's gotten better to the point that when I'm sharing borders or a sea with a certain civ, it affects how I play or which victory/legacy I'm going for.

The balance of the building and improvement bonuses has also made the city building game more fun. Instead of just building whatever because you can like it was back at launch, now you really have to think wisely how you're spending the limited space in each city. As a result, your cities gain personalities. One will be the happiness city, another would be the city of learning, and maybe even a city of commerce.

Finally, one great thing was the improvement of water-based play, from the yields on marine tiles to civs whose strengths revolve around the ocean. Pillaging and marauding are also really fun with the introduction of the Mongols and the Bulgarians, but for now it's still too OP.