Beautifully finished game! It's a really interesting puzle too, a bit like Islanders, but not a clone at all.
The physically based movement is lovely, at least until your island gets too big and rotates really slowly. Maybe increase the torque applied as the angular momentum increases?
Feels a little harsh once you've built up a large island over 15 minutes or so to make one slip up and lose all your progress. Other than an undo or save games, I'm not really sure what you could do about that.
My only other wish is that the camera could be zoomed out a bit. Perhaps under the player's control. When moving downwards, you can't really see far enough ahead.
On the whole, great job!