What sort of magical place is this? There are people, and activity and updates, oh my!
Before finding this, I found a thread at another civ forum, describing this project as dead and abandoned, and I feared the worst.
On what evil site did you read that?

Unless you're refering to the dead and deceased C4AC, which Planetfall is not related to.
Well, on the other hand, it is not motivating for me to post my feedbacks and not get an answer from the chief modder, so I'll have to suppose he has moved to others things and Planetfall version is the last to be expected.
I'm not a social guy. Plus I'm not fond of people who have no mod design experience themselves, saying "you did well, but you can do even better." after playing half a game.
1. the game is very easy. On immortal I expected the AI to take quite some advance on me before I catch up with my skill. I'm 3x stronger than my neighbors... I believe it is because the AI have trouble developing efficiently its base. For example I see it build not that much improvement and it focus too much on windmill.
I don't experience this myself.

The AI builds varied terrain improvements in my games, including farms. Some factions may avoid farms, but that's probably because they're following a pro-Planet strategy. Point 4 seems to indicate you're not aware of the significance/existence of Planet.
For the record, huge maps and aggressive barbarians may be a combination which is especially detremental to the AI. I'd suggest playing on a standard map and without Scattered Landing Pods.
2. despite being in raging mind worms mode, things are very calm... The MW are rare and almost never penetrate into my border. Quite a different experience from SMAC. And no, my neighbors are far, so they are not screening me from MW onslaughts.
Other people say native life activity is too high.
3. I miss an option to indicate I want more fungus. Fungus everywhere please!!
Alas, my attempts to understand mapscripts have failed.
5. Artillery units. Why they can't bombard or have at least a decent retreat %? The way they are, it reminds me of Civ4 vanilla, I feel they can be more fun to play. I miss a bombard button. The suicide attack to do collateral damage way is not very appealing imho.
Depending on what you mean with Bombard, you need the Accuracy or Range special ability.
6. magtube prevented in rocky except if you build a bunker: why this hassle. This is superfluous for me. Also magtube only giving 1/2 .... it is really too low imho.
The goal is to make terrain more important in combat. That's impossible if you can zip de facto instantly from one place to any other. Civ5's 1 unit per tile and ZoC would be better to achieve this goal, but alas, I'm restricted by Civ4's design and AI.
7. APC ability... why it does not add +1 move? Because an infantry in APC will not move faster in magtube than a foot infantry, but rovers will move faster. I don't like much the way they are implemented.
I don't want APCs to have double movement on flat polar terrain.
8. Obsoleting flamethrowers when you get plasmathrowers... NO! For psy combat, I only need the cheapest unit, as in SMAC, where you would have infantry without gun nor armor but good at psy attack. Here you can't do that really, as the cheaper unit is obsolated.
The AI wouldn't understand it needs to build and use the cheap units to attack native life. At least the more costly units are also better against native life. Eg Hyperians come with Empath Song for free, and can pick Plasma Shard as their special ability.