Some operas I have absolutely loved seeing are Turandot (Puccini), Barber of Seville (Rossini), Die Fledermaus (Strauss), and Hansel Und Gretel (Humperdnick). Also, the last two can be seen/heard in both German and English.
Wagner's operas are amazing, provided you don't mind huge blaring sounds. When Wagner isn't being vulgar, his music is simply beautiful. Just listen to the parts with Siegmund and Sieglinde in Die Walkure. 4laugh The entirety of Tristan und Isolde too.
Scriabin is great too, his earlier works are like spicier Chopin works and his later works resemble Debussy, with a surrealistic and slightly romantic bent.
Late Liszt works are good too. I understand some may find his earlier works too flashy, but his pilgrimage stuff and "atonal"(not truly atonal but certainly a start anyway) experiments are hauntingly beautiful.
Donizetti - Don Pasquale, La fille du Regiment, etc
Adams - Doctor Atomic, Nixon in China
Puccini - La Boheme, Madama Butterfly, etc
Mozart - Magic Flute, Don Giovanni, Cosi fan tutte, etc
Gounod - Damnation of Faust
Berg - Wozzeck, Lulu
General classical, I would recommend: