Describing the end of the world in music is no small deal. Wagner took 16 hours spread over four nights when he tried in the Ring Cycle. Jonathan Dove does it more economically in his 75-minute eschatological opera The Day After, but still delivers a sweeping sonic spectacle through music that depicts the cataclysm of a sun-scorched earth in epic terms. And the only disappointment in last week’s staging of the piece by ENO was that the budget didn’t stretch to something equally spectacular to look at.