This was pretty fun and addicting once I got the hang of it. For some reason the [?] on the menu didn't work, which I figure was a tutor. Also found a bug where if you start the game on a level you just lost on, you lose instantly.
Some things I think could be improved with the game is having some sort of special attack with limited uses to help when you get swamped with enemies because once you fall behind, it's pretty much game over.
Some things I would change is instead of having the player lose if the player goes out of bounds, just prevent the player from going out of bounds. Also the player bounds don't match up to the enemy bounds because I've knocked a few over the line, but were not killed.