I saw this film a year ago in Italian and understood nothing. I loved it. Now I have finally seen it in English and understood everything. I now love it even more.
In my opinion, the most beautiful part of Lezione Ventuno is the perfect pairing of incredible music with images that make the notes come to life more than ever before. Beethoven, Vivaldi, Rossini - their music is used to enfold the viewer in a world of shimmering sound. This might not seem that important to some, but seeing as how the movie itself is about Beethoven, music and beauty, I believe it to be the key to the whole production.
The three stories interweave very well, each one complimenting the other and eventually coming together in resolution which was, to my mind, perfect in its tragedy. The story in the mountains had its moments of unexplained oddity, but on the whole was so visually stunning that I was willing to overlook it.
I will admit that this movie seems to be very subjective as to whether one likes it or not. I loved it, but others have not been quite so entranced. Still, I suggest you watch the movie for yourself and make your own opinion.