It was a very nice animation, well-done effects, solid character design, fitting music. I know how long 3-D animation takes and to take it to such a nice level takes a lot of tweaking and adjusting and considering how long you've worked on it, I won't suggest you make it longer, even though I would want ot see a longer animation maybe with a similar concept.
The one criticism I would offer you is that since the story is based around the two characters playing the piano, the fingers (and really the whole rig in general) could've been a bit more flexible, I'm not sure if it was the animator that didn't flex the fingers enough or the rig wouldn't allow for proper bending, but the fingers seemed very stiff to me. I would've liked to see more shots that focus the fingers and you really get to see an exaggerated reaction to hitting each key.