Oh my god. Thank you so much. That's the best advice I've gotten... ever, actually.
My biggest problem in that regard is that my player group is sadly kind of... naive. I had a lot of intrigue planned into the story, but instead of e.g. picking up the notebook of a minion who's managing the trading for a dubious enterprise, which sent killers after them, after I pointed out that there is said notebook, they prefer to go back into a brothel. So I'm a bit frustrated as well, about all the stuff I wrote not being used basically. I ain't nice enough to alter their ending: They are pretty much fucked because knowledge is power and they skipped all information bits. Well, just imagine the attention span of CoD players skipping every cinematic. I have to admit that the group constellation is a bit problematic: 3 guys / 1 girl really motivated and trying to get stuff done and 1 gf doing a cod speedrun.
Kind of another reason for my burnout: frustration.

So i guess, taking your advice, I shall introduce more simple mission design, less multi-layered intrigues. But I'll stick to the bad ending that I wrote. Choices have been made after all. :)

Thanks again. Me venting felt nice as well ^^

Edit: removed the dreadnaught sized post^^