Take what I say with a grain of salt. I am not particularly knowledgable about opera.

I wouldn't say Walküre per se has a stigma attached to it, but Wagner sure has. When it comes to him and his immediate family there is the Nazi stigma. Wagner, the person, is suspect (raging antisemite etc.) but his music is still considered one of the greats, I'd say. He is no Beethoven or Mozart, though.