Pretty dang awesome, though I feel like not many will play due to the boring-looking menu screenshot you've posted. Gameplay feels good, and the tradeoff of losing health vs killing enemies is a creative one that makes for some interesting gameplay moments!
I will note, there's a huge difficulty spike when you get to the boss: the game could use some levels to pad out the difficulty curve, or perhaps if that's not possible then the boss needs to be made easier.
Reminds me a lot of THOTH, this one. Great game! This is the best rating I've given to a game so far.