They also changed Thor significantly from its original Marvel roots. No crippled doctor tapping a stick.
I think the reason they keep failing with FF is because they can't nail Reed. The Thing is easy. Johnny Storm is very easy. Sue is difficult to give much weight to, but a "strong woman" angle shouldn't be too difficult. But Reed they keep screwing up badly. He is the smartest man in the world, and he knows it. He needs to be written as a patriarch. A leader. A beacon. Instead he's written as wishy-washy and unconfident. Awkward. Maybe they're trying for the hero's journey kind of thing, and maybe it's origin-itis. But I gotta think when Reed first strapped into his rocket, he was feeling like a god. Not some dork who gets flustered around the ladies.
Also, when you cast a guy who looks like a high schooler in the role, it's difficult to accept that he has the gravitas of the smartest man in the world.
Reed should be Stark without the snark. A living legend. That might not jive with current sensibilities, but I think that's what you need to pull off the FF - a leader who the rest of the team respects and follows.
And of course, Doom needs to be the monarch of Latveria. How hard is that to understand?