Quite a good game. Hard as f*ck though, or maybe I'm just not playing it the right way yet.
I would suggest to make the disappear time of coins and hearts a bit longer so you can pick them up a little bit easier.
And, I think a brief moment of invulnerability and ghost-mode after a hit would help, because if you now get surrounded you will never be able to get out because you get bumped around, doesn't feel fair.
Also, do hits stack? I've got the feeling that if you get hit by multiple enemies or bullets they all count, ties in with the invulnerability I mentioned above.
But anyways, pretty cool game I keep coming back to :)