Just what is it that you hate so much about the previous two movies ? I own them both, and whilst they're not in the same league as the best MCU movies, they're perfectly competent superhero movies.
They would've been perfectly competent superhero movies in the 1990s. By the standards of their time, they were somewhat simplistic and cheesy. I don't hate them, but they're not particularly good.
The first one suffers mainly because the FF aren't actually heroes. If anything, they act more like villains. The only time they actually try to help other people is when they cause a near-disaster through their own actions, and in the finale, they're only fighting to protect themselves, not anyone else -- and worse, they risk destroying the entire world in order to protect just themselves, the most staggeringly selfish and irresponsible thing I've ever seen movie "heroes" do.
I'd sy any shortcomings are due to the FF themselves, but then, I've never really been a fan...
No, the shortcomings are because the movies didn't portray the FF all that well. They're much richer characters in the comics. For instance, the Sue Richards of the modern comics is a remarkably powerful, intelligent, capable figure, succeeding as an explorer and diplomat and superhero while also being the mother of two of the most powerful superbeings on Earth. Not only is she the glue that holds the fractious FF together and keeps their eccentricities in check, but she's the first person you'd turn to if you wanted a negotiator to avert an interstellar war. Conversely, Jessica Alba's Sue Storm was basically defined by her ability to look good in her underwear. Which was certainly playing to Alba's strengths, but didn't do the character justice.