Most levels are really straightforward, and those who aren't seem to be placed at random. Also, having two or several grids to fill is a good idea, but it is pretty much left out the moment it is introduced, which is kind of a waste in my opinion.
Still a nice breeze... except for level 60, in which I inadvertantly discovered that one can actually rotate pieces. Wow.
Also, I never got my achievements for levels 50 and 60?! Well.