If you haven't watched the trailer yet, don't. The trailer gives too much away and robs the viewer of the sense of constant discovery, and there is a trove of things to discover.
This is a story of an unloved soul looking for a way out of the somber world of his own feelings and thoughts, while carrying the burden of a beautiful mind. Being a theater piece at its inception, the movie ravishes with its dialogues and beautiful scenes. The lack of color is abundantly compensated by the vivid close-ups, the overall suspense and poignant flashbacks.
Michael (the mental patient being the centerpiece of the story) is lovable from the first seconds as a character and as an actor playing the character. Xavier Dolan has a way of wooing people, so it's very hard not to fall in love with his performance and his character by the end of the movie. He's brisk, accurate, hits the target with every line, and when he opens up in the end, the beauty of it is so tremendous it pierces your heart like a golden needle. The performances of the other actors are no less impressive, but Dolan is an inevitable scene-stealer.
Tragedy here is more of a liberation of sorts. The witty and at times funny story takes a sharp turn into the abyss of emotional pain. All the elements fall into place perfectly, creating a feeling that you've just watched a short.
Elephant Song is a masterpiece worthy of watching and rewatching, listening and relistening. It will leave no string untouched.