It is a bit difficult to understand at first what you're supposed to do. On top of that there was a lot on screen at once and I was not sure which rocks were hitting me and which were on the background.
Also, the red and green bar were a bit confusing, may be you could replace the red bar by a currency that is ticking up. Furthermore, the green meter fills up like half way before I even saw the character I was supposed to hit.
I think it also need some balancing, I just spammed the space bar and won most of the time.
The thing I like about most about your game is that the monster design was pretty epic! I love playing as a cool monster.