Good controls, feels solid and quite smooth to play. Music is nice too - are there more themes as you progress?
Some feedback I would give is that the two starting guns seem to be basically the same other than different amounts of ammo; it would be nice to have some more variety between them. The first boss also has so much health; being able to deal more damage, or having them take fewer hits to die would make it feel much more satisfying.
One other thing that isn't about the actual game - it would be helpful to have all the controls listed in the game description - I didn't know it had WASD movement at first and also had to experiment a bit to work out how to swap weapons.
All in all though a cool project - well done!