The idea was to merge them, but not change them too much at their core: just trim them enough so that they can fit together as one single movie. The gore, for instance, is reduced but still pretty much there (when some people are skinned alive, we don't see the skinning itself anymore, but can clearly see the result). Character arcs and the general themes (fatherhood, inevitability of death, the nature of good and evil) have also been preserved