A really wowie and simple concept! The only negative thing I found was that it gets difficult to grab the pieces eventually, because you have pintpoint click on them, so perhaps a bigger grab radius or something would be cool. So that if you slighly press next to it you still grab it.
What would probably also work well would be mouse cursors! One default state and one grabbing state to have some more visual indicators if something has been grabbed.
Overall super solid and polished really well!