Zero Hour was a later reasonably well-crafted but ultimately uninteresting attempt by DC to yet again tap the vein which the original Crisis on Infinite Earths had done so exceedingly well some years before. Here again is a giant threat which spans the entire DCU and which by the end revises substantially much of what had existed before. But unlike the Crisis which arguably filled a need, Zero Hour merely filled a desire for more profits and while that's perfectly understandable for a company to wish for, it undermines the ultimate value of the effort. That and it pretty much failed. Few if any of the character changes which resulted from Zero Hour seemed to linger much past the event itself.
For Justice Society fans though the Zero Hour was mostly regrettable in that once again the mavens of DC tried to off the JSA seeing the vintage heroes as old and out of step, and once again missing the delightful texture to the fictional DC universe the existence of such venerable heroes can bring. DC it seems is always wanting to revise its history and sadly all too often ignoring the rich vibrant history it already has.