I completely understand the idea behind not allowing fleets to wipe out planets without an investment of troops. Its just too damned easy! However, once a race has lost space superiority there is very little that he can do to hold onto planets, even if he must hold one at all costs for JUST A FEW MORE TURNS

I know this won't make it into the final code since they are probably in lock down mode, but I think it would make a damn fine expansion.

1) Planet battles, unless there is an overwhelming advantage should take more than one turn. Since no one will agree on how long it should take, make it a game setting (unless this really screws up the AI)

2) As it stands, the defender is the underdog. That is fine, since it would be a real pain to cough up 40 Billion troops everytime I want to take a planet. However, if I have a planet that I think will be invaded, and I need to hold onto it, for as long as possible, I should be able to fortify it. This could be a setting that will allow me to divert 0-100% of all resources of that planet for fortification for that turn. I can continue to fortify the planet, turn after turn to some upper level (some VERY large level if someone wants to spend decades fortifying a planet) based on population and tech. This fortification bonus gives a very large bonus to defending troops

3) If I significantly lower this amount of fortification, then the fortifications already created, very gradually degrade over time

4) Attackers can directly attack these fortifications from orbit using raw firepower but a) This takes time, b)Each round of bombardment degrades the planet quality a very (VERY) tiny bit, c) As fortifications get weaker there is a level of diminishing gains in continuing the bombardment.

I think this system would add more strategic flavour and give interesting choices to the player. Though much of the AI would need to be modified, I think it would make an excellent expansion pack.