Good game, nice tribute.
First of all, to everyone bitching and moaning about the artist stealing the idea or whatever: Shut the fuck up. Yes, it plays just like Cave Story. So what? Enjoy the game for what it is, and stop whining about foul play. It's a fucking flash game, for crying out loud.
Secondly, I enjoyed playing quite a bit, though I'm playing through again to get this machine gun I apparently missed.