First of all, fantastic product, it is already very fun and strategically appealing. After logging a dozen hours here is my feedback, I will start with feature ideas/negative as they are the most constructive, also I apologize if any ideas are already slated features:
Feature Ideas / Negative
1. Solar System / Planet discovery could be much more exciting. Planets all seem similar in function/atmosphere. The number of workable tiles and planetary stat boosts are great differentiation, but this needs to be expanded on. Endless space did an amazing job with planet graphics, planet types, anomalies, and extensive terraforming to make even "uninhabitable worlds" eventually a key asset, and I think a similar approach would be a boon for gal civ 3. With the current setup increasing the number of inhabitable words would create too much micromanagement. Solar Systems could further share output/shipyards, to make managing them streamlined with more workable worlds, and then allow terraforming and more planets to be used. This item is my single biggest feedback, space games need to make each planet discovered an exciting event full of unknown surprises, and gal civ 3 doesn't feel quite there yet.
2. The invasion technology is too far down the tech tree, preventing early hostile takeovers.
3. The invasion process should take time, with each turn reducing transport and planetary population. This allows defensive response. At first it should be quite slow (think 10-20 turns), and as improved invasion technology is researched this should be sped up to a few turns.
4. Ship battles should not always result in a victory, but sometimes just damage to both parties.
Positive Feedback
1. Beautiful game, from the strategic level, down to the close up ship view, everything looks great.
2. Ship design is incredible.
3. Governing / Production / Research is nicely setup, allows control, but does not require too much micromanagement. Ability to Guard, planetary projects, etc, all make it so you have strategic options, but can also put things on relative autopilot.
Bug (probably known)
1. After defeating each race they still keep asking for peace, until peace is granted.
Conclusion: Amazing game, happy I purchased, looking forward to updates, hopefully this feedback is helpful.