It seemed pretty easy to me, at first. I think that in a lot of the earlier levels, the "blocks" started out very close to their end position, so you could just take the "path of least resistance" and solve the level easily. Then BANG. Level 13. Difficulty seems to ramp up like crazy. I gave up at that point, for lack of patience. It would be nice to be able to skip levels.
The more major thing here is that the block movement is a little too sensitive. Maybe try making the mouse a little less sensitive once the block is "held" by the mouse and being "dragged."
Making this sensitivity extra-irritating is the fact that the block is "dropped" whenever you move the mouse outside of the square "play area." I think it would be much less infuriating if you allowed the block to be "held," so long as the cursor is in the game window. But leave the "block" constrained to that "play area."