What's the hardest Paradox game to learn in your opinion?

I’m kind of unusual with this. I found CK2 really easy to pick up, and Vic 2 not much harder, but to this day I don’t get how Stellaris works, and that’s supposed to be an easy paradox game…

Funny, considering that CK2 and Vic 2 don't really have any good in-game tutorials, just walls of text to teach you the game (mostly why I couldn't get into hoi3 when I tried to, though that may also be from the general complexity of that game)
I can definitely play Stellaris, but I don't think I can win Stellaris. It's a pattern for me with long-running strategy games that have definite win conditions - I can often play competently enough to comfortably avoid defeat well into a game, but when it comes down to sealing the deal in the endgame, there's some crucial mistake I made or aspect I've neglected that leaves me in an unwinnable position.

It's part of why I never really got into Civilization. More recently it happened to me when I tried playing Terra Invicta, when it turned out I had needed to seriously scale up my combat capabilities far, far earlier than I had been.

Ironically I think it's made games like EU and CK easier for me to pick up. Simply surviving counts as a success state, so it doesn't actively punish the player as much for playing suboptimally (at least past the point of absolute basic competency), which lets me get a feel for the mechanics and strategies at my own pace.
I've never had any issues with CK2, Vic2 or Stellaris. But EU4? No fucking idea what I'm supposed to be doing.

There are people who found CK2 harder to learn than Vic2? I found CK2 to be moderately difficult, but Vic2 was utterly impenetrable.

And HoI4 is a weird one for me. I feel like I understand most aspects of it well enough to the point where I could be pretty decent at it, except for navies, which I find so difficult to understand and deal with that it kinda just breaks the whole experience for me.

With navies, I just started to spam out the most modern screening ships I could with a mix of torpedoes and light attack. Then give them air support when you're able.

Is it the best navy composition? Almost certainly not. But when I screw up and send some of my fleet to the chopping block, it hurts less since the screens are replaceable.
Hahahaha same, I have no clue how navies work in HOI4. I've been playing landlocked and/or minor countries so I don't have to fuck with it.

It's been a while since I've played most of these, but here's my experience:

HOI4 and EU4 are both complicated on a width scale. There are a million billion individual mechanics and I wasn't always sure what every button did (this was especially true in HOI4). But, each individual mechanic is actually fairly straightforward, so once I was able to consistently remember the mechanics existed, the challenge became understanding how they interacted with each other. In that regard, I think HOI4 is probably more difficult than EU4, as a lot of EU4's mechanics felt like they existed in a vacuum or only applied to certain parts of the world, where most of HOI4s mechanics had to be used together regardless of context.

V2 has fewer mechanics but they are far more arcane - it's more complicated on a depth scale. Now, instead of trying to find the button that does something, the challenge lay in understanding what the button actually does. V2 also presents a boatload of information that is difficult to navigate and parse, so the challenge once I knew what a button did was determining when to actually push it.

CK2 I didn't have much of a problem with, probably because a lot of the mechanics are more personal thanks to its focus on individual characters. Things make a lot more sense when they are personalized and/or humanized, even if they are describing things that happened a thousand years ago.

Stellaris can go either way, depending on what sort of empire is picked. Some are very simple because they reduce the number of mechanics (e.g. AI collectives not needing food), while others are way more complex or challenging.

For the newer games, CK3 is very accessible, even if one hasn't played CK2, as it retains its personalized nature but also has the nested tooltips so you can get explanations of mechanics right on your screen as you're trying to make a decision. V3 I haven't really played enough of, but I found it only had two really complicated mechanics and not much else.

I have to agree with all of these, although I've not played Stellaris so can't comment on that one. I think EU4 and HOI4 particularly become difficult thanks to the sheer number of mechanics added by DLC. I've been playing EU with a couple of friends recently and it took us until the mid 1700s to learn about the slacken recruitment standards mechanics (we're on 1.33, so before it got nerfed in 1.34 and changed completely in 1.35). To us it just seemed like the AI had unlimited manpower.

I think one of the important things about V2 is actually just knowing what you can ignore. Like you really don't need to look at the prices of individual goods 98% of the time unless you're doing some serious power gaming. It's okay to let your capitalists build crappy factories that will go bankrupt so long as it's not you paying for it.
consistently remember the mechanics existed

even after 1000 hours of HOI4, I still sometimes forget to start building or researching before I start the game 😅

So with just a little bit of time on CKII, your skill skyrockets…thats what the graph shows.

it's required skill, not current player skill

I haven't played too many of them, but I managed to pick up Stellaris really quickly. On the other hand, UE4 felt like the type of game you'd only enjoy if you knew exactly what you were doing. I even spent a considerable amount of time trying to learn this game, and most videos i've watched spent like a solid hour rtc performing pre-game setups in the paused state. It's absolutely insane

1000 hour EU4 player here. My pre-unpause setup takes like... 5 minutes, usually. EU4 has a rabbithole of micro you can dive into if trying to powergame, but a pretty reasonable level of success can be achieved without having to ultra-minmax everything.

That's not to say that EU4 is a simple game, by any means, but as the expansions have gone on, the game has power-creeped to a degree, so it's harder to totally lose than it used to be.

Eu4 and stellaris are fairly easy to learn or to be more specific they are just fairly easy games so even if you dont know half of the mechanics you Will still be able to play them on the passable level, alghtough that makes their ease to learn heavily dependent on the patch since AI in those two games tends to get bumps in difficulty in some patches.

Cities Skylines People:

Victoria 2 hands down. Like taxes? What the fuk do they do, besides giving me more money? What the hell is that economy? That game imo is the hardest out of all.

CK2, cause I've only played CK 2 & 3, and Stellaris.

Stellaris was really easy for me to pick up compared to CK. Maybe because scifi tropes make sense to me and I know next to nothing about history.

I found Vic2 quite hard to grasp, CK2 was hands down the easiest for me

Definitely HOI4. I tried but could never get it, I even watched so many let's plays and tutorials 😂

HOI3 is much harder than 4. 4 is the "dumbed down" version.