So I have a few things, nothing overtly bad just minor things I noticed as I went through this game
- The queue in the research tree could use a UI adjustment when you have more than 10(?) techs queued up and want to move something from the end to the front you cannot see it, so you would have to clear the whole queue to get to that one.
- Could a quick search bar for the research tree be added, say x item requires x research/tech. This would be a quick and easy way to zero into the research needed. More beneficial for newer players that wouldn't know exact locations of all tech items.
- Is it possible to add a way to quickly get to your planet/gravity well view? Say if when you're zoomed out, you could double click on the planets icon and have it zoom you in to the point that the gravity well is centered on the players screen. This is just a minor thing that could make navigation a little smoother in my opinion.
- An audible alert of some kind would be nice when ships are under attack (maybe not for scouts, that would get annoying). But I was managing a planet mid-game, and when I zoomed out I noticed on the other side of the galaxy I'd just lost a fleet that I didn't even know was in a fight 
Additionally, is it possible that along with an audible alert, we could get an icon up in the notifications area that is red/blinking to be an attention grabber for combat happening? Even think similar to Stellaris, when a fleet is in combat it has a perma notification icon, that you can click and it will bring you to the combat currently happening & show you a little screen to show the current balance of the fight/event log of the fight. Something similar to this would be awesome QOL stuff.
- When your camera locks onto a ship in a phase lane, if you manually move your camera with WASD it should unlock the camera. I have noticed that I can move my camera quite a ways manually, but it'll still be locked on a scout or something that I managed to accidentally lock onto.
- There does not seem to be a way to cancel in progress buildings, or replace, for planetary surface buildings. Unless I am missing it.
- The rewards for having culture domination on the minor factions/market races, I feel are too weighted/imbalanced, and can quickly cause a player to skyrocket into economical domination without much effort. These are a great idea to have in the game, but maybe with a lower amount of resources gifted to you, or with a larger cool-down between gifts. I got to a point in the game (mid game ish) that I literally didn't need to accept them anymore because I just had such an overwhelming amount of crystal/metal that I didn't care to accept more.
- The AI could definitely use some polishing, it's a little weird when you get it on the backfoot and it just starts throwing ships at you one at a time, rather than realizing it may be better to build up a small fleet to fight you with. You can literally take a planet, and wait if you want to feed your capital ship some XP off the onesie-twosie ships the AI will send at you non-stop.
-- Wish-list item 1 for me, can we add the EXP to be gained from a ship upon killing it back to the overview in the bottom right hand corner? It used to be there for the old sins and that was kind of nice, albeit not a big deal at all.
-- Wish-list item 2, can we get a post game stats screen again? 
-- Wish-list item 3, can we get options in game setup for larger fleet supplies? I'd love to see just how far this game is able to go in it's current state with running exceedingly large fleets late game
-- Wish-list item 4, - Now that missiles are their own units, is it possible for capital ships to have PDS units to shoot them down? Think how a naval ship would use PDS to shoot at an incoming object. (this would also apply on a lower level to garda flaks)
All in all, I very much enjoyed this, I love the new stellar shift that happens, it causes a good bit of unpredictability, and if you're not paying attention it can really catch you out of position. The UI is generally pretty solid, albeit a little bland which isn't really an issue, more of a taste thing. There was absolutely no lag in the game when running around with 2k fleet supply in a single fleet in end-game. I'm so glad Sins is back!