I remember playing the beta of this ages and ages and ages ago - or at least it seems like a long time ago.
It was the first physics based puzzle game I came across so it's forever implanted in my mind as the title that kicked off the sub genre. Many hundreds of physics based puzzle games were then spawned by this rejuvination of the puzzle game outside of the casual gaming space.
Aside from the clever thinking side, the other great thing about the game is it's atmosphere. The look of the thing and the music actually rekindles memories of drawing when I was a kid, which puts one simple thought into my head:
I've never been able to draw!
Anyway, if you've not picked this up yet in the amazing pay what you want(!) sale you're seriously missing out. Today is the last day (15th jan 2010) so make sure you don't miss out!