Nice concept but...
For your first game, it is actually okay I think. But nowadays, flash games players are getting more and more demanding, hence the required complexity of the games increases.
The gameplay engine is actually good, it's fun killing things, but it obviously gets repetitive since there are no goals, and you are limited to two moves and the fatality.
The graphics are pretty much essential, although I kinda like them.
Music is nonexistant, and even if the original plan was to make it simple, adding a background music should have been part of it. The sound effects are okay i guess.
Basically, It is not bad, but it's only fun for a short while. I see you made a sequel. I'll be sure to check that out, because I like the concept of this game, and I'm hoping to see it more developed.