So i decided to play this for a bit since i almost immediately dropped galciv 2 when it came out and didn't touch 3 and thought: well maybe i was wrong and the new one wouldn't be bad at all. Cause nobody would make the same shit 3 times right? Such a thing has never happened before right?
The laser 1 -> laser 2 -> laser 3 thing improved somewhat, now a new level ocassionaly gives a new weapon in addition to improving existing weapons.
Economy system is best described by this picture:
So at the start of the game i have Earth that has 4 minerals. Production is minerals multiplied by approval and then modified by workers, improvements, etc.
Worker with 6 dilligence adds +6%, one planetary improvement district may add more or less the same (usually more) depending on upgrade level, tech, adjacency bonuses, terrain etc/
Modified Earth industrial production is 4.4.
Nearby is Mars with 2 minerals (+1 if i pick a relevant option during colonization event).
If i colonize Mars (can be done on 2nd turn) and leave it as colony - Earth magically get a +2.84 minerals and now its production is 7.5. Mars if its a colony can't be controlled directly and i don't even hav to pay any upkeep for it.
All the rest of the Mars resources is also transferred to Earth (research, income, influence, food, control) and modified by Earth's population and and buildings same as production.
Now if i make Mars a core world i get a second planet with 3 minerals and industrial production of 1.15 (snce it has 1 worker, no improvements, low approval etc). Also it has 3 tiles for imporvements and nonexistent population capacity so it'll likely never be close to Earth's output. Earth stays at production of 4.4 in this case, and i also need to hire a governor and pay upkeep for colony center building on Mars.
So its like for core worlds the economy system kinda tries to be realistic, but for colonies the extraction and transportion of resources is abstracted away.
I found that usually a planet is either obviously intended to be a colony like Mars (1-3 tiles and population capacity) or a core world (lots of tiles and special resources).
Also since all production is multiplied by approval, an additional entertainer colonist usually increases production much more than an additional worker colonist. (They can switch jobs instantly with no cost). Though that also depends on the colonist since they use different stats for production and entertainment.
Another "interesting" mechanic is anomalies, particlulary "ship graveyard" one. Humans get one exploration ship at the beginning that can investigate them, with a possibility of getting another straight away by assigning a commander to a special prototype ship (is built instantly for no cost, cant be rebilt if destroyed (?), gets special bonuses depending on commander, so like a "hero" ship).
So by exploring these ship graveyards one gets a random free ship in three turns, colonizer, star base consturctor, probe, another explorer ship, or a combat ship. There are lots of these graveyards and the new ones spawn once in a while. Beacuse of them by turn 115 i've built almost no ships in Earth shipyards, have about 6 explorers, built all the starbases that i needed (4 spare constructors relax near Earth) and have so much combat ships orbiting each planet that AI is concerned by my military buildup. And the graveyards keep respawning.
Other than that seems similar to galciv 2. Culture borders expanding through space and "flipping" planet ownership, shitty auto combat with 3 weapon types and 3 defence types, strategic resources like in Stellaris i guess (they are quantifiable so you get +0.3 awesomium per turn from 3 mines and a new ship may require 1, instead of a swordsman requiring one iron mine in regular civ).
This is on version 1.01.343914b that i've got on the high seas, so perhaps something is different in the latest version but i doubt it.
Perhaps worth one playthrough until the novelty wears off.