Hello! for your second (I presume) game this is not bad! However if you want to keep developing it I have a few irks:
The gun menu is a bit strange, adding and subtracting slots doesnt seem like it does much, also its difficult to tell what buttons do what on that screen.
The font is a bit off and using vibrant red and green for it is a little jarring, I would suggest maybe revising your colour pallete a bit.
For the gameplay, I only needed to use the shotgun until level 4, which seems a bit odd, having some kind of gun progression would make the game more satisfying (think boxhead or similar)
Also for the end level screen, the end sequence plays for too short and gets cut off, I understand that some computers and browsers have different timings for this kind of thing but it is an issue.