Not bad for your first game
You did a solid job making your first game and it managed to stay in the portal with an ok score. The graphics are all right for a beginner although you need to work on some details. But what prevents the game from being awesome is that it gets repetitive after a while. Yea, the enemies fire at you, you aim them, fire back, then go to the next level, very basic. Great games do not always have abstract structures, but you need more componets to make the game better. It is hard for a beginner to be masterful, just keep on practicing and you will get better.