I almost gave up on this one because of the characters' propensity for making long-winded speeches about Exodus/Genesis/time travel/twisting logic/bizarre Shakespeare references.
Ultimately, I would consider Zetsuen no Tempest very, very average. The characterization is fairly strong, but the particulars of the world ending are annoying vague and feel contrived. Too much in the story exists because you know the author thought it was cool.
Take it or leave it: it's not a drop-it-like-it's-hot show, but neither is it a must-watch show.