"Wollen wir uns die Oper zusammen ___?"
Because of "uns" in the test sentence, only "anhören" is possible. Even if one might say
only anhören works with this reflexive construction:
And as others have noted, an opera is more than just an acoustic experience, so I would rather say ansehen than anhören (unless of course one is referring to a CD or radio transmission).
As a more general rule you can think of "hören" as "to hear" and "(sich) anhören" as "to listen to". The only exception is for uncountable, undefined acoustic sources.
"Anhören" wouldn't work in that case. But as soon as you are talking about one piece in particular, "anhören" is better.
This isn't wrong but it sounds a bit odd to me. IN questions though either version is acceptable.
I'm no fan or expert of operas, so the term might indeed be
In casual language, one would only use