I liked the style, minimalistic but appealing. The gameplay loop is fun, once you understand you don't have to shoot everything, just the asteriods coming toward you and the enemy ships. I think the game would benefit from some background music, and the bullet sounds are ok, but I would add some pitch variations to make them less repetitive. Overall is a good concept, and match both themes, you have to spin the gun around the planet I guess, and, is there anything more serious that a space rock hitting Earth?