Pretty good. Good on art and audio side. I wouldn't add jump +1 power-up beyond double jump. I was able to fly using jumping. Stronger visual checkpoints indication would be of benefit.
Sometimes a game was boring because it took a lot of hits to kill enemies. This became very obvious during boss fight as despite doing damage boss was barely losing health. Power-ups kinda help but I would make minion spawn rate dependend on your shooting power: smaller power, more minions, until you reach decent fire power.