1. In my opinion these two kinds of entertainment are actually the matter of taste. Nowadays everyone has a chance to watch an opera or a ballet you just need to buy a ticket.
2. Probably if one likes heavy mettal he won't be able to understand opera. Because it is considered to be high art.
3. Too many people thinks that the ballet is the most boring entartainment ever. The actors do not speak or at least sing and you need understand the meaning by the actions on the stage. And that si the most difficult part.