I think my biggest criticism is that it's just... kind of confusing to figure out what's going on. After a few rounds, and playing around with the F1 menu, I sort of figured out what was going on, but it's certainly not fed to you. I suppose that's a good thing, but it was tough figuring out what was causing more or less coins to spawn, what the penalty for death was, what your attack and auto attack buttons did, ect.
Graphics were nice though, and the controls, once learned, were very snappy. The use of the theme was also quite good, not shoehorned or annoying, actually made gameplay more fun, and added a little bit of urgency.
Awesome job, overall!