I have played a lot of 4x games over the years including civs, moo2, endless legend, sins.
I have not yet played multiplayer gciv3.
My first gciv experience.

gciv3 beta 5 feedback

make a new top level tab that includes a breakdown on overall revenue/expenses
trade routes
how many do i have
how much are they earning
how can i cancel one to make a higher earning one

military summary tab which lists all units and is sortable/filterable.
as-is i can lose units

are carriers OP?

***need to be able to queue tech tree selections***

need empire overview screen -
 report with one line per colony
 drill to colony management screen

ship model builder -- i have tried this briefly and it's clunky.  I wish it integrated more into loading a ship.  I want to see my pew pews on the outside of my ship.  Shield too.

overall weapons/defense meta -- this feels a little light.  Is it really just a 4 option rock paper scissors shotgun(carriers) with regards to weapon choice vs defense choice? 
chance to hit and damage vs sheilds/armor -- all of this needs more info on the ship overview or post-battle.
Sheilds counter beams, point defense counters missles and armor counters kinetic?
I remember in moo2 you had ap weapons and weapons that hit shields from 4 sidesn (4x dmg vs shields) and autofire (3x shots with -15% hit penalty), all of which had implications vs defense.  Without playing multiplayer I could be missing the bigger picture on this.

Lest you think I am only complaining, here is some feedback on great things about your game
1. The colony production "palette".  Brilliant improvement over previous systems of directing colony production.  The empire default as well.

2. Looks like the best 4x w/ ship builder since moo2

3. I hope this game is good enough that it can get a good multiplayer scene going.

4. Beta 6 has some nice improvements I am seeing in my first game