Oh man!
This was great! I'm a pianist myself, and I found this amusing and a first of its kind (I think, may have to research on that), seeing as I've never seen something of this concept before. What I would suggest is a few things which would really make it fly forward:
~ When you hold a key down, make it hold instead of repeating.
~ An echo/damper key/pedal maybe?
~ Still make the keys clickable might be useful.
~ Ability to play and hold multiple keys at once.
~ Changing octaves and/or more keys would be cool also.
~ And for key labels, dont just put the sharp name, put the flat name to. I don't have trouble with this, but I'm sure others might =)
Once again, well done on a good concept. PM if you want to chat =)