What do people from the clical music/opera world think of clical crossover & pop-opera singers...?

One of my favorite singers sang rock/pop/folk music in the 60's and 70's and ended up singing Opera in the 80's. She still has a wonderful voice, and I think is probably recognized as one of the few, if not the only pop star to make it in Opera. Linda Ronstadt still does concerts now and again, but I think she is still singing Opera.