For the entirety of the Jack Kirby/Stan Lee run, the Fantastic Four broke new ground almost constantly. They laid the groundwork for much of what Marvel is today.
- bickering teammates
- interesting new locales
- global threats
It's unpredictability was a big selling point. At that point, the Marvel Universe was in its infancy. As the Marvel Universe grew, the things that made the Fantastic Four special weren't as special anymore. With the popularity of the X-Men and the Avengers, The Fantastic Four wasn't as Fantastic as they once were. To top it off, The Fantastic Four is much more prone to stagnation than other super teams. Their shared origin binds them together and makes it harder to shake things up.
Another strike against Marvel's First Family is that people are reluctant to break new ground. Unlike Jack Kirby in the Silver Age, no one wants to create new characters or other intellectual property since it will immediately fall under ownership of Marvel and they'll be left out in the cold.
Barring Marvel changing how they treat creators, I still have some ideas on how to revamp the Fantastic Four.
- The original lineup has money troubles and has to let a reality TV crew follow them around to pay the bills.
- Reed becomes the stay at home mom of the Fantastic Four. The Thing leads the team with The Human Torch, the Invisible Girl, and a new fourth.
- Reed and Sue actually become responsible parents, leaving The Thing and the Human Torch to pick up the pieces. This almost happened with Steve Englehart's run until Marvel hit the panic button.
- The Human Torch steps into a leadership role with three other characters as the Fantastic Four. Johnny's regressed quite a bit since his marriage to Alicia Masters was undone. He's the same age as Peter Parker and should start acting like it.
- A new team with no original members steps up to be the Fantastic Four since there currently isn't one. Imagine a team headed up by the Black Panther or Ant-Man!
- A team of previously unknown characters with a different origin is given the name. Since the Inhumans are all the rage these days, four SHIELD agents exposed to Terrigen Mist could step into the FF role easily.
The Fantastic Four should be the Doctor Who of the Marvel Universe. Much like the Doctor regenerates, the Fantastic Four needs new blood and probably some new faces to survive.