God, how I can relate to almost all of what was written.
I want to add something more; post-campaign-exhaustion or post-game-depression! Every time I finish a campaign I am kind of glad that it is over, sad that it is over, impatient to start the next one and at the same very reluctant to do so. Therefore, yea: documentaries, articles, eu4wiki, dev-streams, forums here, achievement-list, AAR's, Reddit, etc... I kind of go into "absorb information"-mode and start forging several concepts for a new run in my head. That normally takes days, sometimes weeks before one idea becomes so strong that one weekday night I have to fire up the game. And then I am hooked and my girlfriend feels neglected; "ah, you play this history game again".
I also observed with myself that with every campaign I stumble across a few details of the game, that make me think, I am a beginner and have no sophisticated knowledge about anything (after clocking more than 1.300hours...). I.e. I still haven't understood 100% how trade exactly works and kind of get lazy reading through the countless guides, as I only want to know how to maximise income with a few simplified principles. Recently I was wondering, if there is any information about how generals or admirals gain their traits and couldn't find much/didn't really look much either. I always tell myself, "okay, next campaign, I'll try to play more diplomatically smart and collect some sweet PU's", just to end up nervously starting bold wars again focusing on conquering stuff. This list could go on and on.
Worst part is for me: reading in the forums and seeing some truly marvellous campaigns from other players and thinking that my ones are insignificant in comparison, lol.
Out of all the major PDX-titles, I find EU4 excels at offering the best replayability in my opinion.
What a refreshing topic and I am glad I am apparently not the only weirdo, ha!
