Actually, I think trying to do the original Final Fantasy (four-person party of configurable classes) with the Fantastic Four as the Light Warriors could be a great read.
Edit: Looking at it, although the original game didn't do this, you could even map them fairly easily to the four elements. The Human Torch maps very obviously to Fire, The Thing is a nearly equally obvious fit for Earth, "flexibility" is one of the general attributes of Water, and "invisibility" correlates neatly enough to Air. (It now wouldn't surprise me if this had been intentional on the part of the original designers of those characters.)
Edit: Looking at it, although the original game didn't do this, you could even map them fairly easily to the four elements. The Human Torch maps very obviously to Fire, The Thing is a nearly equally obvious fit for Earth, "flexibility" is one of the general attributes of Water, and "invisibility" correlates neatly enough to Air. (It now wouldn't surprise me if this had been intentional on the part of the original designers of those characters.)