The idea is great, but the mechanics aren't feeling really nice. The movement feels like sliding in ice and I never know if i hitted an enemy or not. Maybe adding particles or animations to the enemies when hitted would make the game much more enjoyable. Also the UI could've been better. Make the timer with maximum 2 decimal digits and biger, on the top center of the screen, and the bullets and HP you could've placed them like in common FPS, bullets on the bottom right corner and bullets on the bottom left corner. An the amount of enemies that apear grows insanely quickly.
The idea is great, but it could've been implemented better.