They don't want to stick too close to the origins, because we know three things.
First, cosmic rays in orbit don't give people superpowers, or there would be small towns of superpeople in the US and Russia.
Second, Ben Grimm has to be a little different. The Dead End Kids are a cryptic reference now, not a living image to invoke as Ben's childhood.
Third, Victor von Doom as a gypsy and
king; magician and
scientists; homicidal maniac fixated exclusively on Reed and Sue and
rational genius aiming at world conquest, only works in the comics. You can put one Doom in a panel, then put another in the next panel. In the comics, the reader then imagines the smooth transition from one panel to the next, clearly or fuzzily as he or she wishes. But in a movie the character has to morph convincingly from one persona to the other. Not so easy then. (That's the fundamental difference in "graphic novel" and film that comic book purists like to highlight when they're bitching about adaptations.)
The film adaptations got the personal dynamics right and addressed these other structural problems. We hope the new people do as well.