If I have to choose one record that, for me, is the missing link between heavy metal and opera it is "Delirium Cordia" from avant-garde metal band Fantomas. A project from Mike Patton (Faith No More) with Dave Lombardo (ex-Slayer) on drums. The record changed the way I listened to music. It exposed me to something I didn't know I was looking for. There was no pulse in the music but there was a lot of atmosphere without becoming Pink Floyd. It was more like a soundtrack than a rock album. It was not love on first hearing but it opened doors for me. And one of those doors was opera.