I've just bought the gama and can't wait to get my hands on it 
Since I'm way overexcited, I'm thinking in terms of my own idea of what the perfect 4x star game would be, what would you like to see in such a game? I wonder if some of these will be part of GC3...
- 3D-Galaxy with stars and planets not on a flat map but in three dimensions, plus star map functionality to quickly highlight things (say sector maps, fleet movements, civilian vessels etc., think Caliban from Mike Resnick's birthright)
- The option to generate immense maps, think Distant Worlds with thousands of stars and tens of thousand of planets, if you wanted to
- The option to have more AI opponents, this kinda goes with the larger galaxies, say 40 opponents and the option for some of these to be vastly different (say some can only live in gas giants and you can exterminate every living thing on such a planet but you cannot colonize it, races that can only inhabit, say, red giants etc, think Kevin Anderson's Saga of the seven suns)
- More freedom to come up with surprising solutions (say thew way you can teleport an entire station through an unstable wormhole in Haegemonia)
- Full tactical battle mode - the option to choose whether you direct the battle yourself or delegate that fully or partially to the AI, say I want to personally attend to the invasion of a star system as the outcome of the battle is be crucial, but I want the AI to take care of search and destroy mission to handle two pirate fighters in an asteroid belt). Say the game can switch between full RTS mode if you choose full tactical battle mode or auto as it is in GC2 now.
- Battle mode in 3d (as in freedom of movement in three directions), think Homeworld-like battles plus terrain bonuses/obstacles (say you can use an steroid belt to your advantage or the gravity well of a planet or the radiation of a star), think Ender's game on steroids
- More sophisticated ship building options
- More complicated tech trees and interdependancy and synergy of the techs in plus more race-centric variations
- More control over planetary invasions if you choose to