I do not prefer the raving on the background, but i like the game look. Bullets getting destroyed off the screen is not a enjoyable feature.
Changing islands is very nice feature, because those form a different type of levels and more variety, and also the borders to the each arena comes from the ledges.
It's good you have a way to modify the controls and sounds, so here the regulation of preferences is not the subject of an appeal. I like how you can change the direction of the bullet. I'd like to see more different shoot bullets and on the levels i would like to see some special objects and some ground elevations to make "levels" more interesting. Flying bullets would be more notable to react at them.