what I liked most was the general mood: the tense and dark music that syncs with mobile bars sfx (like the mood of the original space invaders), and as the "mood" element interacts with the gameplay (slow character). Many puzzle games have that cheerful and light tone, but his is a great use of color (Monochrome GB), music, to passes a claustrofobic and oppressive sensation (including there the mysterious ball element that seems to control the situation). I can imagine that everything takes place in a dystopia, or a kind of macabre reallity show (movies like "The cube", and so on).
When the character is slow it bothers me at the same time contributing to the mentioned above. But it bothers a little the gameplay. Perhaps a chance to keep the tense atmosphere, and not and not hinder the gameplay, would be the character appear to respond slower, but in the truth he moves the same amount of pixels as before in the same amount of time. I do not know how you would do, nor if it would do such a difference. Anyway, is awesome that the slow character, and the the increase of tension in music, tells the player that he must be more careful about his moves.
So, it is a simple game, but it has enough gamedesign content. Congratulations.