Having played all iterations of GC since II there is always something that made the game unplayable for me once it really got going: The cluttered map. So here are my suggestions to cure that - hopefully fairly easy to implement. I am also open to suggestion, maybe there is some setting I missed?
1.) The number one priority is the ability to highlight ships or fleets of enemy factions. Often the colors of your opponents are like "light grey", "darker light grey", "really light grey" and "greyish grey" 
(I exaggerate), so picking out the ships and fleets on the screen that really matter (not the myriads of drones and freighters) is near impossible.
We need some "flashing" or or other way to pinpoint enemy ships of factions one is at war with.
We also need "travel history" lines when we click on any fleet, so we can see the direction they have taken.
We also need the ability to "replay all ship travel of last turn" so we can see ships move that we might have missed if we were zoomed in on another part of the map during the AI`s turn.
2.) Please make the options for "showing stuff with zoom level XXX" so that you can see the effects immediately - without restarting the game.
Currently I don´t even know if "slider left" is zoomed in or out... and I have to experiment endlessly and tediously to find the right amount of "slider movement" to give me the desired zoom level where stuff changes from symbol to 3D graphic.
3.) Find some way to make the firepower/hitpoints of enemy fleets immediately recognizable. Maybe add a background colored"blob" around the fleet (this could pulse for enemies, see point #1!!) to show the "might" of that fleet.
Conclusion: The endgame becomes a total, unmanagable mess on the map. It is hard to tell friend and foe apart, see where everyone is coming from or going to and what happened in the AI´s turn (if you weren´t watching like a hawk or save and reload to not miss anything important).
The game starts feeling like a chore at that point and I often quit playing because things are becoming confusing for me to keep up and I miss enemy incursions just because my map is too messy.
Otherwise...having a lot of fun with the latest beta!!
