Thanks for your kind words.
I wish I could take credit for GalCiv IV but I only acted as a consultant this time. Derek (Kael of Fall from Heaven fame) is the lead this time.
Invasions - there seems no way to "repell" an invasion - even if you build defenses (so whats the point?). its just a matter of time.
1. maybe if you introduced a mechanic - something simple like - each defense builds your defense rating and to invade it you must have ship strength/Soldiering > planet defense. Just a thought.
2. Ability to trade star-bases or worlds in trade screen
3 - Consider increasing speed technologies. If you plan on the larger maps - cross the galaxy even with modest tech becomes and undue chore - maybe instead of like +1 moves - make it +2 or +3
Look forward to the enhancements.
For your questions:
1. Sieges will always, eventually, win. However the time it takes depends on the resistance. The idea is that if the enemy has space/air superiority long enough, they will eventually win but you can affect how long.
That said, we are looking at adding non-mobile orbital defenses and beefing up military starbases to auto defend anything in their area which would make military starbases a lot more interesting (imo).
2. So this got taken out. My understanding is that there was just too much exploitation of this.
3. I think the thought here is to have additonal techologies so that there is a more gradual progression. v1.02 will make your ships go a lot faster in your territory.
Cheers!