This is a straightforward movie - a framing story about our young protagonists in musical school, and the opera itself, played out simultaneously after the hero passes some magical gate every day for a few hours. The framing story seemed a bit cliché but never got the upper hand; the fantasy sequences are perfectly realised, with respect to the fairytale atmosphere of the libretto, so not too realistic but rather colourful and dreamlike.
As to the music, well, I'm not an opera gourmet; I rather liked how some of the arias were blared out with gusto and not too fine an intonation, but on the other hand, the queen's soprano really put goosebumps on my skin - it's quite an event hearing such a perfect and dramatic voice over a cinema sound system (pretty loud, too, in our case).
(I'm a sucker for choir movies, btw ... the human voice is the most beautiful of instruments!)
The one thing I didn't understand about the music was the generic end-credits song, why not use Mozart again?
Overall, a hearty recommendation for all music lovers. We liked it very much, even though we're 50ish and the movie is clearly targeted at a younger audience - the school scenes, interior and exterior, are clearly inspired by Harry Potter, they even put in an Austrian railway viaduct similar to the one on the Mallaig line :)