On what difficulty are you playing? Anything below Godlike is TOO easy, but on Godlike, by the time I get to the point where I am finally capable of being on the offensive (around turn 250 on Gigantic+ maps), the AI do have a few planets with a high enough population and decent improvements to where I have to use Core Detonation or Tidal Disruption with an invasion force of 3+ to reach a reliable rate of success. On any other difficulty, however, Information Warfare is just too good..

Improvements that i would really like to see is smarter AIs in general, without needing a ton of cheats to make them competitive. Maybe then they would have better improvements built and a higher population cap on more planets.

Although, I do agree that defensive/military improvements are absolutely useless besides increasing the level of my Hyperion Shrinker. There is rarely a transport anywhere near or headed toward any of my planets.

In my current and last game (both godlike insane maps), I have an AI with one planet that can't be invaded or culture flipped.  I abandoned the last game due to a bug, but the only way to take the AI out was to use the benevolent ideology trait that makes all planets in your zone of control flip.  I don't remember the AI's race in that one.

In my current game, it's the Yor.  I've taken all but this one last planet and have used individual transports and fleets of transports (6b pop each ship) and they won't fall.  They get down to 41.2 b pop and just stop dying.  I've used bio and core detonation over and over and I'm not touching their buildings or pop.

Another AI can only be taken with Core Detonation and 6b pop transports.  Nothing else will scratch their paint.  I'll assume the other remaining AI will be essentially the same.

I'll eventually get the ideology trait and take them all out.  Invasion isn't always a given.

Uh-oh, I already used my culture flip ideology. Time for kamikaze transports. 

MottiKhan played on Godlike, the highest difficulty. It is in the parenthesis of the first sentence.

What we really need is a difficulty rework. Unfortunately, right now, there is a huge disparity between godlike and every other difficulty. In my last game on the difficulty just below godlike and a gigantic map, I purposely waited around for every other race to catch up to me, but they never did. I ultimately got a culture victory with an Ascension victory just ten turns away just as everyone else started touching on Ascension age tech. On godlike mode, I am the one doing the catching up for the first 200 turns.

I'll tell what I would like is the cut scenes from GC2 reworked or a short video of the battleground with the relevant races fighting? please?

I'd like ideology points per invasion too. 

On that last game, I was playing as the Krynn on godlike.  Metaverse says suicidal. The Yor surrendered to the Drengin and I still couldn't take the planet, so I wiped out everyone else and used the benevolent ideology trait to flip the planet.  It was my only option for a conquest victory.

I only got 606 points for that slugfest.  It was harder than all of my other games combined. The Krynn are a pretty weak race. Maybe the weakest.  I would rate it at closer to 10,000.

TBH, the system they have (as with most things in the game) is workable, but the balance is presently off.

As I understand it, currently defense is calculated by taking the planetary population, multiplying it by Resistance, and then dividing it by the number of tiles on the planet. The problem with that is, it's a double-nerf on population - If I have a 20-tile planet with 100 population and 25% resistance, I end up with about 1.25 defenders per tile. 

A 6-pop transport landing on this planet will lose defense % of his troops, and then the remaining ones will all be deployed against 1 tile at a time. Even invading a planet 75% defense, a single transport will land 1.5 troopers. Given attacker casualties rates are always lower than defender casualties, that single transport will likely be able to take 5-6 tiles before it is wiped out using conventional warfare. With any of the tactics which decrease resistance further, or anything that increases soldiering (which acts as a multiplier to attacker numbers), this becomes an automatic wipeout for the defender.

So here's what I think:

1) Defense is too powerful. Defense stat should pretty much never go over 50%, and getting it that high should require a lot of effort (like wonders and player-unique buildings). By combining an Elerium Defense Shield with an upgraded defense shield, you can put Defense to 125%, making a planet effectively immune to conventional warfare, planetary bombardment, and info war tactics, since they cannot reduce the defense to under 100%. This should Never Happen.

2) Resistance is too weak. Much too weak. It is basically operating as the counterpart to soldiering, but where soldiering starts at 100% resistance starts at 25%. This can be completely nulified by some of the invasion tactics. Info War, Planetary Bombardment, Tidal Disruption and Core Detonation can all reduce Resistance to <0%, which should also Never Happen.

3) Invasion tactics should not be on specialization techs. This may be controversial, but the fact is, if you make some unlucky choices you can be put in a position where you cannot invade some planets on a non-tech-trade game. If I throw 100 transports at a planet, that planet should fall regardless of if I use a stupid frontal assault or bombard the planet to bits; the real difference should be in my own casualty count. Specialization techs should instead offer choices between resistance-boosting effects and soldiering-boosting ones.

If we can get to a situation where Defense is never higher that 50% and Resistance is never lower than about that (but can go over 100%), then we might start seeing a more interesting invasion game with genuine arms races on the surface as well as in space.