I really liked this game, and have come back to play again after making it through the story mode a few times. It's simple, but very difficult, and the sound design is great- way better than most submissions.
One issue I haven't seen in other comments is the timing for the sword-wielding enemies on level one. It seems to me like they can deal damage before the animation and sound effect of the sword swing. Since the animation and sound are the two things that give the player cues about timing, those things should come before damage.
It's cool to have enemies generate randomly at each level, but I don't think there's much of a point for enemies to drop random amounts of money for such a short game, where being able to buy power-ups/health is really important, but there aren't enough stages for that kind of variability to matter much. This was an awesome game. Thanks!