Just yesterday I decided to become a founder too.
At first launch the game was slow especially when I wanted to use other programs like browser. Restarted windows and then it was fine.
I know its alpha and I expect lots of things to change but here my comments.
Interface: Im a bit lost it's so empty, way too minimal and working on a resolution 2560x1440 on 27" makes it even worse. Sure I like minimal design but a little bigger graphics, buttons etc. would be better, and if the govern, tech etc. buttons were in the middle of screen would be much better. Als better if words are replaced by logos.
The background starmap its too noisy makes it hard to look around your planets, ships etc.
And the general feel is too dark, and difficult to find what you want. I would like them to pop out more like having brighter graphics around planets and ships, starbases in contrast with a less noisy background.
I hope to see a more complete concetrated/centered interface with less mouse travelling from one point of the screen to another. And some visual notifications when you hit turn and save.
In GC2 I was zooming out from 1st turn because I liked to have the general image and it was easier to find my ships and colonizable planets now this is not so well implemented. Colonizable planets have small or bigger circled in center rather being dots with small holes inside, so I liked the older style better. Some colors to inform the type of planets, ships, starbases would be very useful.
Graphics: Well here I expected more. I'm not fan of lego like ship building, I'd like a sleek design rather having to build ships part by part. Though I have done it lots of time in GC2 and spent hours and hours but I think it's just another mini game in the game with no real purpose more like waste of time. A simpler approach where I could attach just weapons and engines on nice prebuild ships with no decorative parts. And really nice ships... star trek, star wars, babylon 5 to name a few examples.
On the stars and planets... they seem less realistic than GC2 perhaps because I had a mod installed, a popular one I don't remember anymore.
Earth map is poor.. the colors are bad and north pole ice cap is missing also south pole is in gray with no ice too. Well I hope humanity by the time we reach space age we'll have solved the global warming so the ice caps would be still there. Removing them is just wrong.
On other planet maps I have to say they are way better than before but some contintents looks too artificial like they are pixelized.
I don't mention the buildings I'm sure they will be replaced by new ones on final version.
Last on solar systems the planets are too small and remain static no orbiting and way too few 1-2 or none (note that I had set it at abundant planets). I never liked the limit of 5 in GC2 and I hope to see solar systems with 8-15 planets in future. Planets are small and its better for realism but harder to notice perhaps a total different approach with orbit lanes and graphics around all planets of the selected solar system?
The planet screen where a huge moon orbits in the background is too much.
HEX SYSTEM: Ok it's good but I hate when I see my ships going zig-zag perhaps this can be solved somehow? Looks very stupid 
Gameplay: I got bored game was too slow nothing happens so I abandoned ok I know it alpha for testing but my ships were going around and nothing was happening anomalies were very rare compared to gc2 and way too few planets on a large map with abundant stars and planets.
After more than 100 turns I had colonized only 5 planets where 3 of them are missing their picture on planet list on the right. Restarting the game didn't solve it so its a BUG.
Asteroids and resources seems to be unusable at this stage of the game. Buidling a starbase on a resource has no effect.
Something I hoped to see in GC3 was more realism on planets where they are not small islands in space where you can built a few buildings on very limited slots, but real planets with many cities.
My idea of a planet colonization is to start with capital city and build what you want, be limited only by the maximum city size small, large and metropolis. Building 40 factories or 20 research centers whatever you wish except unique buildings where you can build only one per city or planet. After your reach maximum city level you can build another city and another choosing what type of city you want economy, manufacture, research or agriculture. Visual of the planets either from city perspective or from above the planet to reflect the type of planet and change after terraforming. And of course cities are limited by the available space on the planet.
But I guess my long time wish will remain a dream never to be implemented. At least not in GC.
In general the GC3 seems like the new version of a program some better graphics but the same thing there can be lots of improvements and new approach on some things. Looking forward to see the next builds.
