Good game. I have a feedback tho. When player left clicks and you are creating a bullet, you give speed to the bullet in the right direction. But bullet's speed value depends on how far you click.
I guess you didn't normalize the difference of sceen position bullet's initial position.
Therefore when clicking close, bullet is slow. When clicking far, bullet is fast. If you just normalize the vector you use in your calculations, that would be fixed.
I assumed this was unintentional since real guns would shoot everywhere in same speed but if this was intentional, you can ignore this comment. Good shooter game overall :)