This is great! If I absolutely had to make a tweak it would be to spawn the enemies farther away from the player between each wave. I would often lose most of my health between waves as there was no count down timer AND they spawned on top of me. I actually loved that the controls were based on the players rotation. Left was always left as the character was facing, although hard to get used to at first it was a cool and unique game mechanic I really enjoyed!