> The game has civilizations transform into other ones.

This is the most significant gameplay change for this edition, and from a concept point of view it's not a terrible idea, but the execution is extremely jarring. As you progress into the next age the game basically gets a reset. Alliances are gone, trade is reset, city states disappear unless you've pulled them into your civilization, most buildings become obsolete, units get reorganized in a rather dramatic way.

I get what they're trying to do, they're trying to balance the mid and late game to prevent snowballing.
The problem with the way they've done it is that as you progress towards the end of the second age, as a player you have very few incentives to actually build most improvements. Outpace the AI in research and culture, or outproduce them and lay waste to their big cities.

The settlement limit as you go into the second age also tends to penalize early expansion, another balancing measure. You find the "new world" but you can't just go ahead and do the massive landgrab because doing so comes with a set of penalties which you'll have to offset by building things that'll compensate and in turn stunt growth. As you approach the end of the second age that limit is raised drastically which I can only guess is to promote conquest at that point, since the existing factions on the other continent will tend to expand but not be powerful enough to stop you from steamrolling them.

It leaves you with the impression that ages are just designed to stunt growth and expansion and you're fairly confined unless you want to stack penalties. I got the impression the AI doesn't deal with the reset particularly well either, since some AI players which were fairly strong early on started faltering in the second age.

Finally, the ages mechanic comes with an end-age crisis, which rather than an interesting challenge turns into a bunch of busywork. In the second age the crisis I got was religion related, where you get to pick your poison and then deal with your choice. In my case I had a choice to invest into a lot of buildings to boost happiness as the AI sent out waves of missionaries to stamp out my religion, or just churn out missionaries. The latter was cheaper and didn't take up precious space.

> you need to spread improvements across tiles instead of building tall.

I have mixed feelings about this in the long game. It's nice to see cities sprawl out into districts/quarters, but at the same time you're trading resources for growth. Overbuilding is a nice mechanic, but in the end I feel that buildings becoming obsolete at the end of an age makes me not want to invest too much in certain buildings despite having a massive amount of production. A particular game I played I ended up with Rome next to the sea, which grew and grew until there was no room for expansion anymore until the end of the age. Maybe it'd have been better to have one or two more buildings in a district?

In Civ 6 I felt it was a neat feature with some nice gameplay mechanics, but in 7 I feel the mechanic has expanded so much that you're constantly weighing options trying to plan ahead that it weighs things down. Maybe I'll feel differently about it over time.

> I’m pretty happy with Civ VII, and I think popular opinion is 50-50 right now

Honestly, this is the first time I'm really on the fence about Civ. There's a lot of ideas in there that kind of work, but at the same time kind of don't work. If I were to summarize my sentiment in a single sentence: the motto "a civilization to stand the test of time" has been supplanted with the dread of looming impermanence whispering "this too will pass".