This is a fun game. I think you can go places with this. If you have any missiles left, perhaps the bomber might exchange fire with you. I like how that fast plane comes from behind. Perhaps a boss enemy or objective at the end of each level? Bomb a ship, blow a super plane out of the sky? A secret German UFO as a final boss? I just saw the trailer for Iron Sky so it's on my mind.
I get points for shooting the parashootist. It might be fun to splatter him and get bonus points.
I did encounter what appears to be a bug. I started the game and the first enemy was a bomber. It did not die. I have only screenshots, not video I'm afraid.
Here it is at 361 points of shooting.
At 551 points I decided I should call for reinforcements because that bomber did not want to die.