Here is my brutally honest review:
<In order of importance>
- Projectiles blend with ground
- You can click per 1ms (1/1000 of a second; mechanically impossible for firearms as far as I know)
- Enemy AI is incredibly predictable
- Ground is ugly (can easily tell that it is repeating; breaks immersion)
- No enemy variation
- Health bar is very basic
- Sprites were taken off the web (This is OK for beginners in my opinion)
Your game is good for an absolute beginner, make sure to view more tutorials to expand on your knowledge. I made games using Unity, and viewing many tutorials made my games more refined.