L'amore dei tre re isn't exactly obscure, though it's not quite mainstream. It's interesting because it reflects Italian opera in a post Verdi, post Wagner flux, with elements of Puccini and Debussy. It's a symbol of early 20th century Italy, on the eve of the First World War..That war transformed Europe to the extent that any account of music history is worthless unless the trauma is taken into account. Things changed, not simply because fashion changed, but because the world could never be quite the same again. So it's interesting to listen to Montemezzi's L'amore dei tre re and think of its underlying subtexts, particularly the trans-Alpine influences. Perhaps it's not entirely coincidental that librettist Sem Bennelli's melodrama focuses on the relationship between Avito, the rightful King of Altura, and the German Achibaldo, who conquered the land by force. Archibaldo's son Manfredo marries Fiora, who is faithful to Avito. In the murderous power struggle that follows, all are killed except Archibaldo, who is left alone and blind.
There's a new book Essays on the Montemezzi-D'Annunzio Nave by David Chandler who wrote and edited the two key works on Alfredo Catalani, composer of La Wally, both reviewed HERE in Opera Today. Chandler's book on Montemezzi is extremely important because it brings Montemezzi scholarship up to date. La Nave is a swashbuckling saga, with a libretto by no less than Gabriele d'Annunzio. Read more about it HERE. There are no commercial recordings of La Nave, so you'll have to study the score. Or listen to L'amore dei tre re, free on the BBC.