Congratulations for having an awesome first game! The feedback from the shooting it's so satisfying, the glowing of the bullets fits pretty nice and the music and sound effects are very rewarding to hear. My only complaint is that the enemies take a little bit too long to spawn, so maybe a few tweaks on your spawning system could do the work. By the way, the power ups are another win for this game.
(Edit) It seems the spawning rate I had in my first play was different in my second play, the first time enemies took like 10 seconds to spawn and now they spawn in a more fluid way, so for now I find the problem solved.