Looks great Blastar. I hope you will keep on going and make this into a full game. I like too that you are working hard on getting the basic system working before you flesh it out.

Being curious, I have a couple of questions about the implementation. Do you use rectangular/square 'collision zones' for the collision system? Or is there another way to reduce the number of collision checks per frame?

Also when you have a bullet at an angle like this (see image below). Do you do a polygon check or one (or more) box checks? What is the best way?