Its simple and has a clear object, but there are a few problems. My #1 concern is the memory usage, because on my older computer (4 years old, but nice) the game ran a little jumpy because maybe the frame rate is too high?
Also i didnt realize that i could fire a weapon for a long time so all i had to do was avoid the balloons with ease. If one knew they could just avoid them for the rest of the game without worrying about the blimps, they could use that to get a better score with no troubles. So maybe make balloons be more deadly or have a requirement to kill them.