I just finished the game at metropolis lvl, it really satisfied me, but I got some observations and suggestions:

Wars ends too fast, there should be better ballance in "war support". For example it could be depended on units that left in current player/AI civilization. At this moment 1-3 bigger battles, taken one city (or even none) and a huge empire is abble to be vassaled by my country. and gives me 900+ gold each turn what is "fun" but I am afraid drasticly unbalanced. At least on difficulity I played.

There could be nice idea to add somekind of exchannge of money on reserch, some buildings with high upkeep that gives some amount of reserch points.

Another imo good idea would be that units could be healed faster in cities and fortification buildings. Or at least there could be some special districts that heals units faster.

Also war score should rise, even if I totaly conquered some civ, because atm i cannot take civ totaly eliminating it if I do not aquire enough war score before conquering it last spot. Or at least i should be abble to insist on them that they give me open border treaty so i can easly pass throw theyr territory after they capitulation.

Good idea would be overview in reserch tab, information how much reserch i aquire from each city/outpost.

Another idea would be that units could have some transportation mode, so they can move for example twice or triple time theyr movement speed, but they military strenght is decresed. Transport mode could work on roads. In late game, moving across the map is too slow.

Units should be abble to swap they places during combat.

There should be added option to remove district from city view, at this moment the only way to destroy district is to ransack it.

Also there should be somekind of icon where exactly there is a connection between diffrence of the ground hightnes, some 2d icon. At this moment is not clear, especialy i can't rotate the screen.

Acquiring eras is too fast according to current year, at least at "metropolis" difficulity level, I am in Early modern era on 31CE.

Also some print screens and suggestions:

There should be information about effect changes after changing axis towards specific ideologies

Tooltips should be next to place I am aiming so I can see the terrain I target, otherwise its not transparent, cursor is behind the tooltips and i have problem with picking perfect place.

Vassals gives a lot of gold each turn, I am not sure is it ballanced, or it should be like it is. But how they earn so much money each turn (comparing to me at same stage) so they can pay me regulary?

War score should rise even if I totaly conquered some civ, because atm i cannot take civ totaly eliminating it if I do not aquire enough war score before conquering it last spot. At this moment i can't do anything with them... They wont give me they territories because its they end, i cant vassalise them. The only thing i can get reparations

Sometimes unclear path to higher ground, I should be abble to move hex next to me, but i need to go around, it seems to be somekind of pathfinding issues.

Thank You for attention. Really good job with this game! I am very satisfied on playing it even with those little issues. I am sure the closer it is to premiere the more perfect it will be!