Currently (August 2013) the situation is similar to remarks already mentioned - the auditorium is closed for reconstruction (although you can see a glipse of how it looks like as the is a courtain with painted view), you can enter the lobby and some coridors with a small exhibition (entrance fee is 2,5 Euro for adults, children under 18 are entering for free) for having some impresions of opera interiors but probably it is better to wait until 2017 for finishing reconstruction works.
Official website to check the latest news (in English):
