One thing that I absolutely loved and should focus on more in my games is all of the particles that you used in yours. I loved the stars flying past you, the ship's boost, and the explosion when I killed an enemy. To me, this game has a lot of potential with where it could go. It seems like you got the core mechanics down, but I think the pacing was a bit slow. One thing that I think you could change about the first level is maybe having the enemy ships have a swooping motion. One not so slow that the player doesn't have a threat but not so fast that it feels unfair to a new player. Just an idea to give the first 10 waves a bit more spice. For the boss, I would have loved to have been shooting that guy for a good 10-15 seconds before he blows up. Just long enough where I feel like I earned my victory a bit more.
Great start to the game and I look forward to seeing where this game goes in the future!