A poor demo.
This demo suggests that your game is nothing more than stacking things on top of things. The complete lack of depth to the game, along with just a single level, would easily cause anyone to believe they would be wasting their time visiting your site for this game.
I am duly impressed with the physics engine, but it's obvious you don't know what to do with it.
Moreover, it took me maybe thirty seconds to stack the boxes in your demo, and the advertisement promises 6 more levels. Well, I hate to have to tell you this, but 7 times 30 seconds is only 3 minutes and 30 seconds.
Maybe if you had some manner of depth to this game, a good 5~10 levels on the demo, with an additional 20~30 levels in the full version, then you'd have a real game. I'm sorry, but for the lack of depth and length, I can't give you any stars or any kind of decent score for this. It's never good when it takes me over three times longer to write a review for a game than it does to play the whole thing.