'Dark' Fantastic Four? Meh.
The best idea I ever heard about an FF flick was a while back... I think it was Peyton Reed, who did
Down With Love, who was attached to FF at one point. He was talking about doing it as a period piece, with a very
Hard Day's Night kind of tone. I think that would be a great way to go. What FF really needs is a solid, faithful take that skews as close to the feel of the Stan & Jack original as possible, and I think that so much of that feel is inextricably tied to the era in which it originated. 'Dark' or 'gritty' or 'realistic' have no place in a Fantastic Four adaptation.
(Well, maybe a
little bit of darkness in Ben's case, as he struggles to come to grips with what's happened to him. There were times early in the series where Ben was just about teetering on the precipice of being a Hulk-style outcast, wanting the 'puny humans to leave him alone'. But I wouldn't want to dwell on that too long--to get the classic FF tone, you need to have Ben finally evolve into Aunt Petunia's Favorite Ever-Lovin' Blue-Eyed Nephew that we all know and love.)
Fantastic Four needs to tend far closer to
Batman: The Brave And The Bold than it does to The Dark Knight. That's all there is to it.
And I'll tell you what else--you need a production designer who can really bring Jack Kirby's visuals to life. Reed's lab gear and gadgets in the last two films? Unimaginitive second-rate Star Trek stuff (NTTAWWT...

). I wanna see some Kirby Machines, darnit!
--g