Above you will see a video of World of Keflings which demonstrates the musical cannons in the game. So, basically, looks to me to be a more complicated version of Mario Paint.
That's not a complaint, mind you. I've whiled away many afternoons just cruising from one tune produced in Mario Paint to the next. From the demonstration in the video, things could get downright ridiculous once players start mucking about using the game to make music themselves.
Too much work for me, but I'll glad sit here and wait while all of you be creative and make cool stuff for me to enjoy later.