This is a really awesome concept, and being able to use your own music is definitely a welcomed feature. Some songs can be a bit overkill even on normal difficulty.
Feedback:
I can't tell what exactly is the hit area of the character. The screen does shake to emphasise it but it's not very clear. Some shots will pass through the head or legs (especially in moments where I can't dodge it at all) but no damage is taken. Perhaps change the shape of the character or the hit area? (I haven't made flash games in a long time so I can't remember or know if it's been changed.)
The controls, the mouse is most likely more fluid than keyboard but during some hectic songs, you 'may' panic to dodge and sometimes the mouse goes out the screen (even in the dimmed light mode) and ultimately you stop moving altogether. Maybe add a border that's not part of the game but just to prevent the mouse from going out of the game screen. In pattern 3, I tended to keep to the edge of the screen and I'd stop moving very so often.
I hope to see more improvements or sequels to this.