Crazy, mad, screen filling action that realizes "hey, you're going to get shot up here" so there's some grace taking hits. Continuing on with the plink of a quarter makes this an addictive mission to complete the game. Stages are laid out in the beginning, so you know how far you're going. Wild power-ups along with my favourite maneuver which I'll call "wall rolling" where you can roll your plane against a wall to shoot in a circular direction. This must be incredible as a 2-player game and will have to try it out. Creative, inventive 'boss' fights.
A few touches would've landed a perfect 10: Some kind of story with a beginning, cut-scenes, and an ending. Perhaps building up your plane or customizing would be a cool feature.
Overall, very refined fun!