pcool, how far you got without fail? Some of the challenges need quick thinking and reacting. The blocks aren't quite perfectly aligned or spaced or there's some unstability so I was surprised by how they acted on collision. Then again I guess that should've been predictable having seen how hard it was for mythbysters to crash those trucks head on.
ed: I got the "?" levels unlocked now. The difficulty and design was just right, didn't feel any frustration except maybe doing the bonus version of 32 where I had to redo a couple time.