Good stuff, I think the difficulty curve was spot on.

It's a nice relaxing puzzle game

The interpolation between squares is a bit weird since the arrow key only works once you've come to a complete stop. Overall a nice simple puzzle game once you get past the controls and stuff. I like the feeling of the triangle sliding into place for each level. Having some sort of indication of failure when you fill the whole with the circles instead of just restarting the level like normal would be nice.