This is a very interesting concept. I had a lot of fun!
I would like to suggest letting the player keep control of whatever block they are moving even if their mouse leaves the block's area. As it is, it's frustrating to be moving blocks in a hurry only to lose control of them because the mouse left it's area. Especially with a camera moving perpendicular to the block's movement.
I would also suggest expanding the block's clickable areas a little bit.
Other than that, you have a pretty interesting idea for a game. I can see it being expanded on. Having different types of walls, like maybe one that falls back down if the player let's go of it, so they need to keep holding it while the character passes underneath.
Nice job!