Cool game, art and sound works well. Would nice to have a hit effect on the enemies, just a red tint is enough. Agree with more level and maybe introducing the different enemies over those levels, this could be a complete game.
Thanks for the positive feedback and suggestion, I'll keep it in mind. The systems I wrote would make it very easy to add more levels and more enemy variations. I'm pretty busy but hopefully I'll have time to turn this into a full game at some point.