English is not my native language, so all this was translated by my mind + the help of a translator))
if English is your native language, and you are not too lazy that to help, you can write to me PM and we will fix it all together :-P

And now.. What "New generation of the World" do:

(you can forget helpless pirates and get ready for pirate mayhem)

if the empire does not destroy the pirates from the beginning, they will develop very quickly

1. pirates will eventually build up to 3-4 stations per system (4 types of stations). And these pirate stations can be deadly for unskilled players.
2. after some time, the pirates will build wandering fleets that can capture neighboring systems and start the same construction there too.
3. if the pirates get too strong - they can offer capitulation and humiliation for the empire (in exchange for their leaving).
4. or they will not offer surrender, but will turn into a pirate crisis, which will be even worse than the coming of the horde. But I will write about crises separately.
5. the strength of pirate fleets and stations always depends on the strength of their prey. The stronger the victim, the more dangerous each fleet and each pirate station will be.

Now, if you capture/occupy planets, there will be a check on how happy the population lived on the planet before you arrived. Or you doing purge? Or you is slaver? and e.t.c.

If a rebel camp does appear (the corresponding icon will appear on the planet), it will start preparation for the uprising and will interfere with your control of the planet (will lower stability and resource extraction).

1. the empire can strangle and destroy the rebel camp if it keeps a lot of armies on the planet and in every possible way raises the stability of the planet
2. if the suppression of the camp will fails, the rebels will strike. The strength of the uprising will depend on: how long the rebels have been preparing (the longer, the stronger they will be), how much population there is on the planet, how bad the occupier is in politics, etc. (the strength of the rebellion will be affected by about 15 checks)
3. if the uprising loses, then the occupation will most likely be able to destroy the camp, or the rebels will survive and begin to gather forces for a new uprising (all this is affected by stability, the number of armies of occupation and how bad the empire of the occupiers).

(factions dissatisfied with your rule will now plot against you. In addition, other empires can help them - through new spy operations)

1. You will see this through new icons that will display the power of the conspiracy on every colony where they appeared.
2. if the сonspiracies against you will become too strong - they will start to affect the entire empire, and you will see new empire modifiers.
3. Faction Conspiracies affects - theft of resources on the planet, the growth of crime, the growth of piracy in the empire, the chance of terrorism on the planet, the chance of rebellion
4. empires can fight with conspiracies in the following ways - by increasing the happiness of the population, and by increasing encryption (if plots are due to spying operations). Or .. just deal with the consequences (reduce crime and piracy).

(in the new generation, it is an ancient mining corporation that has unlimited money and that thinks only about its own interests, completely ignoring the interests of empires).

1. they will build geo-exploration and study neighboring systems for minerals.
2. after which, the construction of expansion fleets will begin and the corporation will try to take away systems with these fleets.
3. in captured systems, drones will study planets for minerals, and where they find them, they will build mining fleets and stations.
4. if the neighbors will resist and do not give up the systems, the drone corporation will begin to allocate more resources and the next attack fleets will be more and more dangerous.
5. if the empire clears too many systems of drones (captured systems are also treated by drones as their own)

then the ancient corporation can send a demilitarization squad to this empire (which will try to destroy all your large stations, and then fly back)

(dangerous to the owner, since your spy operation may fail and your spy may be caught, tortured and killed. If that will happens, you will lose your envoy and you will have fewer diplomats for a couple of years. + political consequences. )

but... if you succeed - these spy operations give just the strongest effects

1. Spy operation - to spread confusion and discord on the planets. You can start or strengthen faction conspiracies on 1-3 planets of the target empire.
This operation can be run repeatedly and enhance the previous effects.

2. Spy operation - arm the separatists. This operation can be launched after 2-3 successful discontent operations.
This is a very dangerous (you can lose a spy) operation. But if you succeed, the separatists on the planet will be armed, and the uprising will be spectacular.

3. Spy operation - spread the virus of insanity. Works great against gestalt consciousness. And this operation can be repeated to enhance the effect of the virus, which will engulf the entire empire.
But.. after your first success - gestalt consciousness will strengthen the protection, and each new attempt to spread the virus will be more dangerous for you, by a complete failure.

1. AI empires are now very actively building small, medium and even large defensive platforms + ion cannons, near their stations. It depends on the resources and the size of the station. The larger the starbase / orbital ring, then the more dangerous platforms they will build near.
And not infrequently they can fight off your top fleet - only with one station. BUt.. only rich empires )) not resource bums.

2. if the enemy is nearby or neighboring systems are under occupation - AI empires will now be very active in building ground defenses. They will destroy other buildings and will build strongholds / fortresses.

If everything is too bad, then they will place the second, and then the third stronghold. And capturing planets, now is a difficult task.

3. In case you didn't know, every empire has a personality (like Evangelizing Zealots, Honorbound Warriors, Peaceful Traders etc.)
In the new generation of the world, all empire personalities will become tougher over time (after year 50 and after year 100). Aggressiveness, Bravery, Military spending all this will grow with time and you will feel this ;)

4. resource shortage or surplus? AI empires will very quickly start trading or rebuilding districts.
The most important point here is: AI empires are now very active in buying alloys.

5. stellaris is over 5 years old, but AI empires still do not improve their fleets and only build new ships without improving old ones (and the player doesn't even notice that he's winning against his neighbors, not because he's strong, but because AI empire uses level 1 technologies in fleets when they've already learned level 4)
This has been fixed too. AI empires now - always upgrade old ships as they research new combat technologies. This dramatically increases the difficulty of wars with AI empires. Since they are now - always improve their fleets.

6. improved AI preparation and checks for the construction of mega-structures. As a result, AI empires start building/rebuilding dangerous mega structures 50+ years earlier than in vanilla.

7. now, ai empires are very active in all espionage ops, including new ones (in vanilla game ai have used only 3 from 10 ops)

8. enlighted primitives and separatists, after rebeletion - now, not a helpless empire with 1 system, but now they can arrange a beating to their neighbors.

9. if the empire is blocked by neigbours and cannot build new stations... Blocked empires now increase their espionage activity several times against their neighbors and significantly strengthen their fleets.

10. if a player or empire is too strong or hostile - AI empires will now very actively begin to take resolutions against the threat (in the vanilla game, empires looked only at themselves (80% of situations) when deciding whether to vote or not. Now, in addition to themselves, empires are looking to see if the resolution will benefit or harm their opponents).
in addition, they will choose The Custodian and then the Emperor much faster.

P.S.: I don't remember what else I added to AI empires, for 3 years of modding)) I wrote only 10 points that immediately came to mind.

(are now perceived as real space monsters that interfere with the first 30-40 years)

1. space amoebas now reproduce by fission. Once every 3-5 years, 1-2 small amoebas are born, then again, then again, then they grow up and in the final, a new group of amoebas separates from the amoeba group.

2. When a new group of amoebas separates from the amoeba group, rolls random whom they will be. Now are three species of amoebas:

Amoeba Hunters: have the largest aggression radius (125), they very rarely give birth to amoebas, and they attack space whales and empires that they meet along the way.

Lazy Amoebas: have the smallest aggression radius (75), they give birth to amoebas very often, and they very rarely move between systems. This species is the most dangerous (since it most often gives birth to other amoebas).

Amoeba borderless: have an average aggression radius (100), give birth to amoebas on average, and they can ignore bordering control, when traveling between systems.

3. if wandering amoebas will fly to the player at the beginning of the game, there will be a lot of problems. So, a lifecycle constraint has been introduced. The more amoebas neutralize the stations, the weaker they will become, up to complete weakening and death.

4. amoebas and space whales now have a self-preservation instinct. The more the empire destroys their groups, the stronger will resist the next ones.

(wormholes are now very unstable and creatures from other galaxies can seep through them)

1. once every 5 years, random guests will pass through a random wormhole in the galaxy. Wormholes, which are often used, are more unstable, and someone can get out through them.

2. 15 kinds of guests )) it can be Patriarch (new leviathan with unique mechanics), it can be amoeba swarm (7 groups) with collective consciousness, it can be merchants, with very unique mechanics of stealing, running away, strengthening themselves, and then returning to their galaxy, buying a new fleet and coming back as an armada. And 12 other kinds of guests (i'm bored to write all them here).

3. most guests will not like your galaxy and when they will finish their scripted activities, they will leave it. But there will be those who want to stay in your galaxy forever.