Simple and kinda lame, but that's okay - I can live with that. However, it is impossible to reach all the balloons by level 3! The cannon ball doesn't go far enough to touch them, making the game/level impossible to finish
Shortcut ... the coins lose value over time, but you cant die, so just hang around the very top of the screen with your lasers all aiming right at you. That way, as soon as the enemy dies, you get the coin at max value. You can upgrade in very little time.
You need to make sure that enemies don't spawn right on top of you and kill you. There has to be a fighting chance to survive, rather than just random dumb luck. A larger screen and smaller ships would be nice too. Other than that, it's okay.
In addition to reducing selection/load times, we need to be able to add or subtract from shield and ammo so we can achieve the best mix. Also, visible ranking would be good. Also, more info on weapons re: power, rather than just shots per min - seems like the intro gun is the best.