Had a lot of fun discovering things, I have now played every faction to the point I start to steamroll. Starting from easy and then switching to hard. So here are some thoughts in no particular order:
AI is eager to declare war when they sense weakness but does not follow up, and are content to just sit there one system over and wait. Do they not have the range tech? Do they assess fleet strength incorrectly? Do they get stuck trying to build enough troopships to take over every single planet simultaneously? I don't know but they seem way too passive in wars.
The construction curves upwards very sharply meaning that most of the game destroyers are too expensive and suddenly you start pumping out loads of heavy cruisers. Maybe some tech or orbital that makes destroyers and light cruisers economical and useful even in mid-game?
The game is structured so that you have a very long build-up period of colonizing, and then a single big battle followed by a long mop up. I usually don't waste resources on invading planets, as these resources are better spent on making sure your fleet can win the initial big battle and then zoom as fast as you can to their 2-3 factory worlds and neutralize them before they can rebuild. Maybe give planets garrison ships ala. Total War? Would make steamroll harder and create more interesting battles.
I had an fun game where I was locked in a very unfavorable corner and Yoral declared war on me very early, so we had an arms race for 50 turns were we stacked low-tech ships in absurd numbers on each others borders. But then the Yoral just send half their fleet to die against a random marauder base, making it way too easy to roll them over.
AI needs to learn maneuvering and focus fire, right now I can take on several times larger AI fleet and win with no losses. They need to direct their fire on the smallest/most damaged ship first and to try to hit it from the side witch has lowest shield percentages. Right now spinning your ships after firing to change the shield side they hit feels like cheating.
AI does not refit old ships (or if they do not aggressively enough), also it would be cool if the AI designs would counter yours (like not using PD if you don't have missiles/fighters or prioritizing shields if you go full beams).
I think difficulty settings should be remade so easy->normal, normal->hard, hard->(give AI even more help)
More map types where you could have choke points like galactic arms or clusters.
Orthin Heavy Cruisers look so sexy.