Ironicaly, most of the so called "metal opera" bands have the most horrible female singers, and their vocal lines are ridicilous. The few good ones are active for one EP usually ( I really liked Sonata Nocturna. For some reason, they sound as if they were trying something completely new, though it's as cliche as can be. And their combination of piano and bass-guitar at the end is awesome :
http://www.youtube.com/watch?v=NcZCfnrluvY )
It sucks.