Love it or hate it, opera is always a great topic to write about - whether as backdrop to romantic and ironic fiction, or as a seething cauldron of ideas for warring experts. Operatic history is not just 400 years of masterpieces; it's the seeds great composers sowed - for performances worth watching, and singers worth hearing - and it can be heaven, or plain hell. The finest writers about opera here are an Olympic roll-call: from Rousseau to Brecht, from Proust to George Eliot, from Berlioz to Debussy.