Very nice game!
It helps that I am quite good at this and managed to get to the seventh level on my first try! What's also great is that this game has very impressive original designs. My only complaint is that the controls with the mouse do seem to get a bit difficult. The music and everything else was very well done. My biggest word of advice is to simply work all around the gunfire when the boss is there. Even if you simply randomly fire throughout that part, chances are you will get some good hits in.
Each enemy seemed to have a very unique attack style to it as well. It was fairly hard with how you did not keep the powerups that you got. At least you were able to keep the upgrades consistent. It took me awhile to notice that you were even suppose to collect those blue dots the enemies left behind. The music is stylistic as well.