Definitely needs some balancing, but I like the idea here and had a lot of fun playing.
A few things I'd say to improve:
- Some kind of reticle or line to help see where I'm aiming
- More forgiving enemy spawns - at the start of some levels and after jumping into pits I'd get ambushed with very low chance of survival
- Auto fire - tapping repeatedly gets tiring, especially when tapping as fast as possible is the best strategy
- Collision glitches - enemies got stuck in walls, and occasionally time pickups fell through the floor