It’s been a sensational week for opera in London, with a sensationally good performance of Strauss’s Elektra at the Royal Opera, and a sensationally terrible production of Fidelio at English National Opera. Charles Edwards’s production of Elektra is revived for the second time, but this is quite the finest account of it, thanks above all to the conducting of Andris Nelsons and the assumption of the title role by Christine Goerke.