Any comic book geek out there is likely aware of all the negative reviews surrounding the newest Fantastic Four film, and I've read plenty of remarks about how Fox needs to quit trying to reboot the film and let Marvel Studios get more control so that studio can figure out how to make it work.
While it's true that Fox doesn't want to give up the distribution rights to Fantastic Four films, that really isn't the problem with poor films about the superhero team. Switching full control to Marvel and Disney isn't going to solve the problem by itself. All one has to do is look at the Marvel Cinematic Universe, which has it shares of weak films. Incredible Hulk is forgettable, Iron Man 2 was a mess and Thor 2 was not good at all -- and in each case, you had a different company who held distribution rights at the time the film was released. Fact is, any studio can distribute a bad film.
And while it may be true that Sony's unwillingness to cede distribution rights for Spider-Man led to a reboot coming too soon, there's no guarantee Sony turning everything back to Marvel and Disney would have solved anything (and nothing is guaranteed now that Spidey will be part of the MCU). Besides, the second Amazing Spider-Man film suffered from the same problem the three weak MCU films had, and the Fantastic Four films have: Subpar writing.
Let's stick with Fantastic Four. The problem with the first film released to theaters was that it had the right idea of being a lighthearted film with a dark undertone, but it had the wrong execution with lightheartedness. Rather than letting the characters drop one-liners here and there and drop a humorous note when the time was right, it went for too many visual gags and put the characters in embarrassing situations. I never saw the second film, but the latest reboot decided to make everything with a dark tone, and that makes movie goers weary when every single superhero flick has that tone.
Furthermore, the first film did a poor job executing the relationship between Johnny Storm and Ben Grimm. The former is supposed to be enamored with his superpowers and be reckless and impulsive, in contrast to Grimm, who is not happy with his superpowers but mostly does things by the book. In the first film, Storm is turned into a jerk who picks on Grimm just because he can. Additionally, the first film didn't effectively portray the relationship between Reed Richards and Sue Storm, in that the two really like each other, but Richards wraps himself up too much in his research that Sue wonders if he really pays attention to her. They instead did a love triangle with Victor Von Doom and it didn't hit the same notes.
Speaking of which, Doctor Doom is the other issue with the Fantastic Four films. It's understandable that you aren't going to make Doom's origin what it was in the comics (a mysterious dictator of an Eastern European nation, which dates back to the Cold War), but in the first film, they made him a greedy, egotistical businessman who was a bigger jerk than Johnny, but failed to make him sympathetic to a degree. The first Iron Man did a better job of taking an egotistical businessman (Obadiah Stane) and making him a little sympathetic, because you can sense he wanted to run Stark Industries after Tony Stark's father Howard passed away, only for Tony to take over. It's a trait that people can relate to (I'm better qualified than the person who got the promotion or who runs the show) as opposed to a general stereotype that the common person can't really identify with (businessmen are greedy because they are).
If Fantastic Four is ever going to succeed as a film franchise, it simply needs writers who understand how to write a lighthearted film with dark undertones and how to make the personalities play off each other, while keeping the superheroes likeable. Trying to reinvent Dr. Doom is a tougher challenge, though, and that may be the biggest hurdle to getting Fantastic Four to work in film.
But while I've wondered whether or not Fox will come to a deal to get Fantastic Four tied into the MCU, that has more to do with what Sony's thinking may be (tying Spidey into MCU will get people interested again) and less to do with it improving the quality of the film. And if Fox decides to tie it to the X-Men, it does need to keep in mind that the Fantastic Four should be a contrast to the X-Men (many of them are supposed to be brooding, although some to a lesser degree than others), not just another group who finds nothing but despair.
To the point, though: Fantastic Four needs to be done in the vein of Guardians of the Galaxy if it's going to work. GotG got it right with doing a lighthearted film with dark undertones. Fantastic Four needs that, and it starts with the writing, not with the studio distributing it.