Very fun game, but There is no possibility for expanding in this game. Needs a point or "money" system that allows you to purchase things like weapon and plane upgrades that allow you to get further in the game. The game allows the in app purchase of new planes that are upgraded, but I will not spend money on a silly little game. Played for about 20 minutes, and now it's played out - DELETE.
To the developers: I am representative of the majority of "iDevice" game players. Give some type of reward for shooting down planes and finishing waves (keep the plane reward the same, but give a bigger bonus for each wave finished) and allow those rewards to be spent on upgrades. you will hold people's attention for SO much longer than this game in its current iteration. I hate to see such a well made game interface so poorly executed. You're on the right track. Keep improving.
Incorporate possibilities for upgrading your plane and getting further in the game and you'll have a winner. As is, it's "meh" at best.