Hmmm. I played Stars! quite a bit in the past (still have it in fact). So I'll expand a bit on Rob's points above. Feed 'em to the troll if you like.
1. Planets
Stars: Each star has one planet, with habitability based on Gravity/Temperature/Radiation levels.
GalCiv: Multiple Planets per star, with habitability based on PQ level.
2. Species
Stars: All species including your own are totally customizable.
GalCiv: You are always Human, and the Aliens are always the same species (Minors will vary). You can however customize your abilities and political party (and the AI will customize its settings too).
3. Ships
Stars: Each ship is custom designed by the user. Ships can be formed into fleets and combat takes the fleets into account.
GalCiv: Ships are all predesigned and become available with the research of certain technologies. You can make fleets, but they function the same as stacked units in Civ (Attacking units fight the strongest one in the stack, then the next strongest, etc, until it or the stack is destroyed).
4. Research
Stars: User sets percentage of total income to contribute to research, and which category to put this money into. Research then advances through generic levels of that category, with new technologies becoming available at certain levels.
GalCiv: User sets percentae of empire spending to contribute to research, and chooses a specific technology to put this money into. There are varying branches of each category and many interconnected prerequisites. User can also achieve victory by researching an ultimate technology at the very end of the tech tree.
5. Resources
Stars: User can build mines on planets to increase production of three core resources, and uninhabited planets can be remotely mined by special ships. these resources can then be moved via freighters.
GalCiv: Aside from special resources located around the glactic map (more on that later), there are no resources. Production is based upon alotted military or social spending at the empire level, which is divided among planets based on population and any production bonuses provided by planetary imporvments.
6. Starbases
Stars: One starbase may be built per planet. The starbase serves as planetary defense, shipyard (depending on starbase type and size), fast transportation (via stargate to another starbase with a gate), and mass driver (interplanetary combat or resource transport).
GalCiv: Starbases may be built anywhere on the galactic map. They can then be fitted with various modules which boost abilities such as trade income, influence, stats of nearby ships, production on nearby planets, etc. If built on a special resource, there are modules avilable to increase the empire-wide bonus provided by it. The starbase can also be upgraded into a Terror Star, which gives it mobility and the ability to actually destroy inhabited star systems. User can achieve victory by making his influence the dominant one in the entire galaxy.
7. Planetary Improvements
Stars: Only generic improvements such as factories, mines, defenses, scanners, etc. can be built. Alternatively, the planet can build any ships or starbases (new starbases will replace a preexisitng one at that planet) that you have designed.
GalCiv: Many varying improvements are available. Each provides bonuses to certain local abilities such as production, morale, planet quality, and influence, in exchange for a monthly maintenance cost. User can build ships on the planet at the same time as improvements, and no shipyard is required.
8. Diplomacy
Stars: User pretty much cannot negotiate with AI players.
GalCiv: User maintains a relationship of various closeness with each species he has encountered. He can also initiate trades with the AI (and the AI can initiate trades with him) which may involve money, influence, planets, technologies, ships, starbases, and trade goods. User can also ally with AIs after fostering a strong friendship and researching the appropriate technologies. User can also acieve victory by allying all Major species.
9. Trade
Stars: User cannot trade with AIs, except for the option to offer ships full of resources to random travelling traders who will give new ships or technology in exchange.
GalCiv: User can construct freighters to establish trade routes with AIs (both Major and Minor species). These trade routes them provide income to both involved players and increase relations between them.
There's more than that, but that's all I can think of at the moment, and I've got other things to do. Still, this should help put the troll in his place. As is, it's pretty obvious that he hasn't played EITHER game very much at all
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