Fantastic puzzle game.  It takes a simple concept (spreading colors to adjacent shapes in order to get them to their goal color) and expands upon it in brilliant ways.

This is not a puzzle game that allows for random clicking until you eventually solve it.  It forces you to understand how the mechanics will affect things and to deliberately manipulate things to approach your goal.

The sound is also excellent, (warning: grossly overused buzz words ahead) being an ambient/atmospheric procedurally generated soundscape that responds to your actions.