As the director of “Green Lantern,” Martin Campbell was far from the first, and certainly not the last filmmaker to deliver a stinker of a DC superhero film. But 14 years after its release, Campbell is unafraid to be honest about its shortcomings — especially the ones he takes personal responsibility for.

M arvel and DC have spent their entire existence trying to convince fans they are galaxies apart, despite orbiting the same comic cosmos. Yet, every time they clash at the box off