I dunno, I can't say about not being explained, just being explained poorly. Yes, you don't have tutorial, but you do have explanation on most of mechanics in game. Though, it would be quite helpfull to make an actual Civpedia for that sake, I hope Amplitude would revisit this idea one day.
Politics are mystery to me too, I can agree on that, but I can't say there was much of a trouble with it. I mean, most races are predetermined to have 1-3 different political branches to follow, and their pops mostly support that, so you shouldn't actually suffer from your main party not being elected, as it will be most definetelly the one you will benefit from the most. But if you decide to create much more diverse empire, that sure can start to be a trouble, although, bonuses from races can cover it (potentially), without even mentioning special minor faction laws. So what with the politics?
I didn't understand about "building in your system". Who is doing what to your systmes?

P.S. As one wise men said-"We can talk hours about strategy, metagame, and the eternal question we always return to. Is Endless Space 2 balanced? No, it is not". Cheese is inevitable, so lactose intollerant are out of picture. Though, IMHO, cheese is core of any long-session strategies-someone preddetermined to skyrocket, and AI cheats in classical 4x fashion.

Originally posted by Punker:

I didn't understand about "building in your system". Who is doing what to your systmes?

Probably a rival outpost, of another faction.

Originally posted by Cpt. Haddock:

This is the darksouls of 4X you learn by dying. Nothing is ever explained properly, getting attacked but can't fight back, tough luck scrub

Fun fact but ES 1 is slightly harder to play.

The learning curve is what I find fun about these games. It means I can get a lot of playthroughs learning new things and optimizing. Then I can gradually add in the DLCs to learn new things and I get a ton of playtime out of a single investment.

There's way too much to pick up in a tutorial, that's what tooltips are for, they explain the things you want more info on when you're ready for more info. If you turn it on the tutorial guy explains quite a lot as you play.

The Fandom wiki is pretty good for the game as well if you need more detail.

Turn off all DLCs, this goes for all Strategy games like Stellaris, Civilization etc.

The base game has already enough complexity and depth for you to learn the basics. I usually buy all the DLCs just to disable them for the first 50ish hours, play every faction at least once and then gradually enable a single DLC and play that for multiple playthroughs.

This will make sure you not only understand the DLC, you also will be able to disable the DLCs that suck and actually know WHY they sucked because you have a grasp of the basic game.