More suggestions

2) Sensor techs should affect the planets.  It's pretty annoying to have to create sensor fleets.

3) Please auto obsolete ships when a better version is made.

Opportunity cost???  What is the opportunity cost of building that extra research lab, factory, etc., only to have Drengin shock troops destroy all that production and enslave all of your Torian women and children because you would not build planatary defenses?  In the real world, we have to spend lots of resources on defense that could have been spent on more video games, cars, restuarants, etc.  If nations weren't taxed for defense, we might have more in our pocket for that extra video game, but what good is that extra video game when ISIS is beheading your neighbors down the street because you wouldn't invest some in defense??

Now if defenses are ineffective and not worth the cost of forgoing another factory, lab, etc that is a balancing problem.  In other words, if the benefits of that extra lab, factory, etc. clearly outweigh the benefits of some planet D (perhaps because you can build more ships and more technologuical ships to keep troop transports from even landing then that is a balancing issue.  However, I think that the game needs to force tough strategic choices on you and deciding to build some D on a planet vice another factory should be a tough choice you have to make.

The benefits of another lab or factory on every planet DO significantly outweigh the benefits of planetary defense on every planet.  If you're letting transports hit your undefended planets, you've already done something wrong.

I keep hearing this "I want choices" defense of bad design.  Let's compare to Civ.  In Civ, cities are not limited by "City Quality", though they may be limited by terrain.  Any city can be made defensible, given the investment in resources without gimping the production of the city.  If you build walls around your city, you aren't eminent domaining your factories and shutting them down.

Same with Master of Orion.  There was none of this slots being taken up garbage for ancillary buildings.  

That's the key.  These are all ancillary.  There's a whole category of buildings which are nice to have, but you'd never in your right mind build them because you're turning your planet into trash to do so.  In GalCiv3, you get the super fun choice of turning Earth into Mars and turning Mars into something that there's no point in defending.  As if planetary quality isn't already terrible on anything but abundant.  Maybe I want to defend Mars.  My cost there should be the time I spend building defenses.

So, if you want those buildings in the game, give planets room for them or put them in orbit.  But don't throw them up as a false choice.

I see your point, but limited buildings is a fundamental design of galciv that probably isnt going to change.  Similar to universal sliders production vice planet by planet production and research specialization which I dont agree with.  I think by having some planets have some building slots and others having more, it forces you to value the bigger planets more.  I think that is the intent.  To really want those planets with more slots.  Afterall, it does make sense.  A bigger planet with more resources can support more infrastructure.  A bigger planet with more land and more favorable environment can support more farms than a tiny ball of rock that cant support any farms but perhaps has the potential for incredible mining.

Also, if you are letting trasnports hit your undefended plantes, you are either doing something wrong or perhaps lossing in a desperate battle against advanced AI.  In other words, you should not assume stupididty for letting transports hit undefended planets.  Indeed 4X games are all about the big picture and opportunity cost.  Perhaps an advanced player allows a smaller world to be invaded because resources are needed for a bigger fight and a bigger war.  I am willing to bet the best galciv players fighting against the toughest AI have planets fall to planatary invasion every now and then.

Also, although civ lets you build unlimited buildings, it only lets you build one thing at a time.  While you are building walls you aren't building something else, say a library, that had it been completed many turns sooner, could have led to more advanced technologies.  But alas, you chose to build a wall instead of a library in the year 1220.  So that tough choice thing is most certainly in civ games.

Yes, the building one thing at a time constraint is there in GalCiv also.  That's what I'm proposing as the better alternative for choice here.  Think of how much better a game that would be.  You could still have interesting choices there.  You could build sensor buildings.  You could make pop growth buildings that don't instill regret as your planets near insta-fill with population.

Here's why planetary defenses will always be worse than another factory or another research lab.  Because it's highly conditional.  Yes, it's a big bonus IF you get hit.  But factories and labs?  They're a big bonus no matter what.  And if giant ships with huge laser beams on them keep you from getting hit, that's all the better.

Heck, you want the EASY solution?  Make Planetary defense a project that just ticks up the planetary defense rating.  Done.  Not as cool, but it'd still be better than as is.

While I agree with the probabilities you have discussed here in that another factory or an extra lab is a sure thing whereas planatary defense may or may not ever be used, I disagree with your quick assessment of how big the bonus is which is highly conditional.  You see, if planatary defenses happen to keep the dredngin from taking a planet with 30 slots, that could be a HUGE HUGE HUGE plus that just might keep you from lossing the game.  Sure, if you build some labs and factories, the extra production is a sure thing, but if the drengin narrowly take a huge planet from you in a desperate fight, you might wish you had some planet defense and not the extra production which is meanlingess now that it takes you 100 turns to recapture the planet.  Every game is conditional and different.  In some games, it might make sense to never build planatary defense, in others, you might be a fool not to at least upgrade defenses at least on planets that "border the neutral zone" so to speak.

Look, lets agree to disagree.  I think limited buildings is ok for this game.  It makes planets with more building slots more vaulable and worth sacrificing huge fleets of warships for.  Yes, other games like civ let you build all buildings on each city / planet, etc., but think I limited buildings forces stragetic hard choices on you.

Lets hear some from the founders like the penguine avatar dude ? or dudette? assumming he/she takes a break from listing bugs for the devs to address.  Excellent job by the way blue penguine avatar founder dude or dudette!!!

When his invasion fleet beats your defense fleet ... quick, scorched-earth your own farms and rush-buy some Planetary Defenses just to soak up more of his droptroops.  Then he'll have to pay 4 transports per planet, instead of using 4 transports to take 4 planets.

So maybe it's fine that Planetary Defenses takes a hex.  Most of the time, you build social stuff instead.  Only planets that are actually in imminent danger of invasion go into panic-build mode and replace a few hexes with defenses.  This is historically accurate

Static defenses that are created well ahead of time generally don't help much;  in Earth history, they typically fight the last war.   See Maginot line.   Of course the sturdy walls of Byzantium keep that city going for 1000 years, but that was in the ancient/middle ages period.   Of course the Byzantines kept paying off their attackers, which was probably more important than the walls.

Mobility, firepower, and flexibility are the key words.  There used to a good strategy that involved forcing the opponent to attack you where you were strongest, because historically the defense had advantages (see Pickett's charge).   But that was then.   In Galciv I firmly believe that you should be attacking rather than defending.  If there is some colony or key point you just can't afford to lose, garrison it with ships.  You have a crack at transports before they unload.  When the danger is past, you have a fleet to attack with.   In the alternative, you have tiles with defense that have to razed and rebuilt, even if they managed to hold the fort.

Well, that's my attitude.

I disagree with the initial concept that the Civilization approach to defense structures is inherently better than the GalCiv approach.  It is different, yes, for all the reasons pointed out, but it can easily be argued that is a good thing.  It is, after all, its own game.  This is the Internet.  Some of us like it both ways.

Being different from Civ is not a crime.  There's nothing wrong with that.  What I don't like is the way the design makes non-critical buildings (i.e. non production, research, influence) almost not worth it to build.  That's all.  And I think Planetary Defense falls into that category.

I think it is really hard to evaluate this with the current AI and without planetary invasions in anything near their final form. It may turn out that planetary defenses are critical, especially on planets near your borders with other civs.