I really loved everything about this game. The colours were really nice, the shooting was satisfying, but I think you could've made the very first red triangle enemy a bit easier because it moves very quickly. I also think it could've benefited from audio, because I sort of lost interest because it got so quiet.
All in all, I think this game does scream 'wow this was done in 3 days?!' so very well done.
Best of luck :D