Wagnerians are like elephants: they never forget. Though the Royal Opera House may have become less conscientious about printing performance histories in its handsome red-covered programs, for many the memories of past Ring cycles at Covent Garden live on. That may not always be a healthy thing – there are of course few more necrophiliac artforms than opera – but it’s impossible to view the opening of Barrie Kosky’s new Ring in isolation. Only the elderly will experience the weight of this being the start of Covent Garden’s ninth postwar Ring cycle, yet many operagoers in London remember at least two or three preceding productions, so where does this one stand?