A really fun and good game.
It is rare to see such an original idea succed so well. I played to the million and was entertained the whole time.
The concept is easy. The gameplay is not much harder. You can play without thinking much on the game. You have done this and yet succeed at making the game fun. Punch to the sides to hit the shapes. If you are low on health, start with an uppercut. I like that you can afford to punch down sometimes despite the name of the game. It makes the gameplay more interesting because it is easier to hit the shapes that way, but at the same time it is much riskier. This could be a good idea if you just try to get a high combo. I got a bit dissappointed when I compared how much score I got at a high combo with how much I got with a low. It seems like there is no difference and that the combo is just there as a side goal besides scores. I found it more fun to go for a combo than to go for a score, so the is nothing to complain about the gameplay.
Some other notes: At sixhundredthousand points the game started to lag and the sounds played in a weird way. It was nothing too bad and I could continue like normal. It was a wise choice to include a pause button, because stuff is happening all the time. The graphics are great and the sounds are cute.
Only suggestion would be to switch background to something that does not make you motion sick. It was a good choice to put a background so the player could see which direction they are moving in. The background that is now is good in the way that it is not so disturbing. Maybe make the squares eight times bigger.