the slaughter high score did keep when i lost all rage but the multiplier didnt :( 
i got to 80x multiplier by only standing still XD 

Not a bad game! It was fun playing it. I got a multiplier of 18.
Just some feedback:

But the optimization for graphics is extremely poor. Literally when there are 4 human running towards me the fps drops immediately when I kill them. This make it very hard to gain multipliers.

Also I would suggest either separating the health and the rage bar, decrease rage bar limit or increase the loss of rage since the enemies didn't pose any immediate threat and the constant amount of human being spawning makes me don't have to care about the ending of rage. This kinda makes the game oriented to getting more multiplier (Although that might be the intention).

Anyway nice game keep up the effort :D