I find GS is a great addition overall, but, as others have said, some things came up short. Balance is obviously an issue, but I haven't seen much discussion here on climate change, which is just riddled with problems. The temperature raises way too quickly, as do the stages. Additionally, the overall effect seems too minimal. A rise in 3 degrees Celsius, and minimal flooding (it seems not enough tiles can flood, even at the highest stage). Snow tiles don't melt, and other terrains don't change either (like plains becoming desert due to drought). The droughts we get are laughable, as they have no long-term impact. No heat waves. Climate change escalates too quickly, but hardly affects anything.
Furthermore, there is little in terms of reversing climate change. All I saw was carbon capture (after getting a science victory, after climate change maxed out), and that has little effect and comes much too late (not to mention it should be in the tech tree, not the civic tree).
Speaking of the tech and civic trees, I really hate the randomness. Makes it hard to plan, for example, for reverting climate change.