If I remember correctly, the levels are procedurally generated, correct? The game has an interesting way of randomly placing keys and locks without making the level impossible, something I haven't been able to figure out. I think the visuals do their job well even those they are 8x8 sprites. One recommendation I have is to give the player more than one life. It is a bit frustrating to see all your progress erased just from making one mistake, even if it's just a small one.
Also, I think I somehow broke the block counter :P
http://gfycat.com/TameSpeedyHammerkop