I didn't have huge issues with the original F4, initially anyway, when I saw them in theaters. No where near the heights of Spider-Man 2 and X2, but they tried to find their own corner to market, and I guess on paper the idea of Marvel's First Family as a kind of low-key family friendly-ish series makes some sense. But they could have been way better.
Honestly I think the same of the X-Men, they've delivered some good movies, some of which I enjoy very much and a few of which are exceptional. But as more time has passed it becomes apparent to me that these are not the X-Men I remember or envision when I read their books, it is Singers interpretation of those books. Much like Nolan had his own interpretation of Batman, which was outstanding. Singer has a solid grasp on the X-Men, but bends the mythos as we know it to his will to make his own. Days of Future Past making for an excellent entry into the X-Men franchise, but still further down the Singerverse rabbit hole and farther away from the source.
Fantastic Four needs a team that understands the concept. It can have an Interstellar vibe, like the new film was trying to shoot for...from the trailers I saw, I didn't see it yet, but they took the wrong inspiration from that film. F4 needs that sense of exploration and wonder, and like Interstellar and The Martian, Theory of Everything, Imitation Game, A Beautiful Mind...somebody that can bring out the excitement in watching a genius problem solve, so we can watch Reed's or Susan's gears turn.
I think both franchises would be for the better in Marvel's hands, but I trust Singer to finish his run. Fantastic Four however, needsto go back. Pronto. Marvel has done well with finding the right person for the job, that has the vision that brings the Marvel Comics version onto the big screen. They've gotten better with their picks over time, and they have a lot of new players taking the reigns for the Phase 3 films...so depending on how the next few years go, their knack for it may even improve.
It would be a shame for the franchise to stay buried because of others incompetence when there is a great movie in there, with all kinds of potential. And considering how Deadpool was made, getting the official green light for a second time due to fan reaction to leaked footage, after being put on the back burner; Fox may see the profitability in cutting a deal like Sony did to reinvigorate that brand, knowing fans will turn up if it's up to their standard, and if it is an all around quality movie, the GA will too.