Very clever ideas introduced in a sensible manner with rising difficulty. Easy to understand, hard to solve - basically what all puzzle games should be.
I'm not a fan of turrets/bullets mechanic at all (I'm not saying that it's a bad mechanic, just one I didn't enjoy as much as others), but that's because I enjoy my puzzle games in a more relaxed fashion.
Some early levels with blue no-scale zones were cool, but gave out the solution too much in the way the normal path was carved :D So it was just a matter of following the dark path and scale along the way :)
(I was also getting slight Baba Is You vibes from the graphics :))