Operas don't remain in the repertory because they have great librettos. They remain because the music is great.Just for fun, a few operas with great music that somehow haven't quite become repertory staples because of their librettos:
- Ernani Lots of great, dark-tinted, Don Carlos-like music, but an unbelievable, confusing, poorly-structured libretto that ends with the hero committing suicide. What?
- La Forza del Destino has not exactly dropped from the repertory, but has been replaced, more or less, by Don Carlo. Why? Because modern people mostly don't buy the whole fate thing, plus the careening plot and Preziosilla are both a little hard to take.
- La Fanciulla del West has absolutely glorious through-composed music....and the libretto, which isn't by Puccini's usual librettists, is a dog. It's undramatic, it has no real climax, the ending is mild....woof! I predict that after the round of Voigt-inspired revivals it'll go back into hiding for another 15 or 20 years.
- Pelleas et Melisande. The exquisite music just isn't enough to conquer the obscure-to-most, allusive, undramatic libretto. It'll never be repertory standard.