Not terrible
It's not the worst shooter ever but it could be better. If you were going to do the charge thing you should have made it so your timed shots could blast every plane on a pass if you aim just right. It seemed like you were kinda doing this but a little more striaghtfoward style would have helped. Or maybe if it took a while to charge it could be like a powerful shot. Otherwise it would have been ok with a more rapid fire rate and maybe some different hit point enemies. Some more levels or just more time with a difficulty progression would have helped also. I just think it was a little plain as it was.