Why would you ever go and see an opera written in the 1950's which smacks of child abuse? Well, it does the soul good to confront the horrors of such evil. So its not a comfortable evening at the opera, but Benjamin Britten's score, and Myfanwy Piper's simple but powerful libretto does other things to the soul - it ravishes the senses. I think its because the tension is so great, because of the dubious things that have gone on between the characters, hence it hightens to awareness of the stunning music, played by just 13 musicians.
If you have never been to the opera then its probably not a good one to start with - if you are a newbie try Rigoletto, also at ENO