I don't usually write reviews for popular countries because it's covered so well (and by better writers? :)) but then I realized the Margravial Opera House doesn't have many yet, including some people who failed to check that it was under renovations for 5 years and still wanted to visit. In fact I did also want to visit it during that time but a simple check online told me it was closed so I postponed to another trip to Europe. It might also lead to the fact that there are few reviews: it was inscribed in 2012 and then almost immediately closed afterwards, 5 long years of renovations followed and it seems almost unfair to do that to a newly inscribed site that gets more attention that before but I suppose it could have something to do with getting grants under UNESCO inscriptions, who knows.
Upon first entry you will be wow'ed by the beauty inside. There isn't really much else though. It's a regular opera house and the staff will explain to you all sorts of features that aren't uncommon in a theater. Pretty much all of it is made of wood which makes the house super susceptible to fire. After a video and the introductions from the staff you can ask questions or just admire it on your own time until you are lead back outside. It's not as strict as in Padua but they do try to keep things going. As the opera house is much smaller than the pictures make it seem you don't really need that much time. It's also interesting to note that the opera house doesn't at all look like one from the outside. There is a story behind that but I'll let you find that out on your own visit.
I give it high marks for beautiful interior but don't see why it's that unique.