It is really cool how that you have different enemies and power ups in there. That game is really cool :-).
Because I am always happy about constructive feedback here are some ideas which I have:
- Add animation (maybe with particle effects) to killed enemies - so that they don't just disappear. E.g. you could reduce their scale to zero over time before removing them from the scene
- Make other enemies harder to kill. E.g. the red enemy could require 3 shots before it is getting killed
- Add Left-Mouse-Button = Fire. Then you could play it completely with one hand
- May having a Boss =)
I like the style very much and you should think of providing a mobile version of it. I think the gameplay is really intuitive and with one finger players will learn it instantly.