Not only is this game a copy of a flash game buts it looks like crap. Been done.
Having played the demo, I'd say it's a very soothing game, but there's not much substance to it. There's like what - 5 operable parts? In terms of getting the mot bang for your buck, you might find your $20 better spent on World of Goo. Still, Crayon Physics Deluxe is a pretty neat little tech demo.
This game was quite enjoyable, but the solutions do lend themselves to abuse. I assumed it was a puzzle game, so I approached it with the goal of "find the first solution that works". Even if there are multiple solutions, that's generally the goal of a puzzle game.
In my opinion, this game is more of a sandbox game (toy) than a puzzle game, because there is almost always a trivial way to solve the "puzzle". The real challenge comes in limiting your actions (which the additional game modes help with) or finding creative ways of solving it (something fans of Fantastic Contraption can appreciate). While this is no less fun, it's not the expectation I was given (especially considering the challenge of the original Crayon Physics demo's limited abilities), resulting in me rushing through the game with some mild disappointment. Now that I've unlocked the further challenges, I believe things will be more enjoyable.
All in all, it's still a great game, but $20 is a lot to ask. That's more than Portal, and Portal took longer to finish and was even more fun to play. You could even get something like Penny Arcade's On The Precipe of Darkness for that much. A comparable game, Fantastic Contraption, only costs $10 to unlock the full functionality (though the main game is available for free). I believe this is a more reasonable price.
this reminds me of fantastic contraption :D