I am a long term Galactic Civilization player and plays a lot of strategy games. One of my wishes was for GC2 to be multiplayers, but to no avail. I was glad to see that GC3 does have the capabilities

With the understanding that this is a Beta which you are reminding us at every start , here are my observations after a full game at normal difficulty.

Needs improvement:

1. Ship Designer
1. No way to keep selection to add again (always need to select weapon back). Didn't see any key/click combination to keep selection after placement.
2. Obsolete button doesn't show on all or most models. You do have a delete, but I didn't want to do it since I still had some ship for a model or two. Makes scrolling through a list to select a ship to build in the shipyard a pain.
2. Shipyard
1. Anyway to upgrade with constructor or something to boost defense? Maybe planetary defense is added to it's existing defenses.
3. Invasion
1. When an enemy is invading, you get a message and you have no clue what planet is being invaded.
2. Always have to scroll to get information.
4. AI
1. Keeps creating colony and survey ships.
2. Way too easy to beat at normal.
3. Keeps asking every turn about making peace.
5. Starbase
1. Once a constructor enters a star base you can't retrieve it. 
2. An indication of how many modules can be added would also be nice.
6. Multiplayer
1. Works well in general. Just gets disconnected for no apparent reason here and there during the game. We just reload and everything is fine for another hour or two.
7. Technology
1. Technology tree is a bit frustrating right now. If you find a technology you want to get and double click on it and it is not in the 'currently available' choices, you will find that the system selected the first 'currently available' technology. It also doesn't give you how long it would take to research it knowing the path to it after clicking once on it.

The Likes:

1. Shipyard: Love the concept!
2. Planet improvements: Bonus from adjacent improvements is a simple idea that works.
3. I like the principle of the technologies with 3 inerrant choices