The time slowing down is a great gameplay mechanic.
I like the primal sounding background music, which I think fits the game very well. The knife hit sound effect is also very meaty and adds to the impact. I think adding some audio effects when picking up the knife and throwing it will enhance the feel and feedback.
Not sure why, but I had trouble picking up the knifes even though they were moving so slowly or just lying on the ground. At first I tried to stab the enemies by walking up to them with the knife in front, which didn't work... LOL.
Also, I think some enemies were killed by their own knives bouncing off trees rather than the ones I threw.
Overall, it's quite a fun concept with a lot of potential to develop into something really cool!