A neat game, I think! ^_^
A few thoughts, if I may:
- I would like an easier way to restart the game on losing; right now it seems, at least, that the only way to restart is to reload the page.
- I'd like to see a bit more fanfare on defeating a boss-level--some particles, or an animation, or something. A bit more of a reward for completing a level, in short.
- Sound effects would really make the whole thing a bit more impactful, I think!
All that said, I enjoyed this overall! The controls are smooth and responsive, and the gameplay is simple and yet nevertheless enjoyable. ^_^