fun
Cool game, but it needs more
What you have right now should be the arcade mode, or endless mode or w/e you want to call it.
With that you should include a single-player "story" mode. not saying there should be a story, just that you should have a set of levels with preset stars in different shapes, different frequencies of enemies, time limits etc. And that way you can pick up at the beginning of each level if you die.
That'd give it a lot more replay value and fun.