Great game! I agree with others that this could go from great to unbelievably awesome by adding a campaign mode where you upgrade your plane, switch planes or something. Select mission types to earn cash, medals, etc.
I can appreciate the attempt at a meaningful story, but the lack of in-game choices to be made ruins it for me. It is more of a challenge to try to NOT win this game, which is kinda lame.
Best strategy I found was 3 clerics in the back row healing constantly with a sword hero and 2 knights in the front row to soak up damage and slowly kill everything