start with a smattering of different operas from different composers:
don giovanni- mozart
carmen- bizet
tristian und isolde- wagner (i think? lol drugs)
tosca- puccini
porgy and bess- gershwin
The Ring Cycle by wagner too
Ballet is easier to take than full on opera sometimes too.
The Firebird - Stravinsky
Romeo and Juliet - Prokofiev
uh forget more
don giovanni- mozart
carmen- bizet
tosca- puccini